She will certainly try convince Nim to open the door at your request. The module gives the option of her 'helping' you persuade him so you get advantage on the persuasion check (and you have a higher modifier than her anyway) 

Mana steps forward and lightly raps on the door and calls forth in his most soothing voice.

”Nim? Nim, are you there? I’m here with Valletta and I’ve brought you back your bird. Nim? Nim? Please open the door.”

Persuasion: 26

Oriace moves with soft, almost spectral grace behind the group. At each lull he offers a slow, reassuring nod, the polished onyx brooch at his throat catching the lantern-light like a half-seen eye. Finally at Nim's door, a calm pulse of thought brushes Mana’s mind—Steady, friend; your words sing truer than any spell—and the halfling lets a faint smile tug his lips as Mana knocks on the door. Hands resting lightly on his drum, Oriace stands ready to greet Nim with courtesy and careful questions once the door swings wide.

Bardic Inspiration to Mana. 

Sterling stood ready, trying his best to conceal his concern as he awaited the door opening. It wasn't that he thought Nim had "snapped" or just decided to hurt others out of the blue--what would be the point?--so much as he never again would simply believe someone just "wouldn't do that," when untoward influences and motivations abounded.

The bard didn't put his hands on his blade; but he did leave them by his side, ready to react the instant trouble appeared.

You hear the lock click, and Nim opens the door. Valletta explains that despite him understanding common he can't speak, but he has developed a simple sign language that she can interpret for you. The attic is cluttered with tools and inventions in various states of completeness. 

Mana smiles at the automaton and extends his hand which holds the remnants of the mangled clockwork bird.

”Thank you for taking some time with us, Nim. I am Mana, this is Wagner, Oriace and Sterling. May we return your bird in exchange for a tour of your workshop? Perhaps you could tell us about some of your creations through Valletta? We’d love to learn more about you, as well.”

Mana waits to be invited into the room, but he does scan past Nim to see how large and complex some of his musings are at this stage. From the door, does what can be seen look like trinkets or anything scaling up to wagon sized?

He is glad to give you a tour. There is a lot of unfinished designs, including a couple of larger ones such a wardrobe that you can walk into and it will put your clothes on you. As well as smaller things like a ball that you can throw against a wall and it will always bounce back to the thrower (which works most of the time). There is also more mundane items such as a phonograph. The more mundane items are all finished. 

 Sterling scrutinized the designs as Nim showed them around. Thinking, he turned to their host with a smile. "Impressive. These must take quite a long time to complete. Which one are you working on now?"

He points to about 6 different things, some of them are are barely started, one is almost finished. If asked about the purpose of the almost finished one he shrugs and signs to explain it doesn't really do anything useful. It was just some entertainment. A machine that just turns itself off 

“Nim, have you been in contact with any other nimblewrights recently? Perhaps one or more from the wizard that brought you here?”

Nim admits (through gesturing to Valetta) that it built another nimblewright to ease its loneliness. But then Nim’s creation fled in confused terror a month ago, and Nim hasn’t seen it since. In light of this revelation, Valetta angrily orders acolytes to remove Nim’s tools and unfinished inventions from the attic, while she forces Nim to look on. As they are clearing it, you see a 1-foot-long copper contraption with an umbrella-like metallic protrusion at one end. It looks complete but wasn't mentioned in your tour of inventions. 

Mana purses his lips as he contemplates the failure in the flight of the bird. Surely this new nimblewright didn’t fly away.

Nim, did your missing friend have a name? What is it?

Was it an event or a flaw in construction that caused them to flee in confused terror?

When they left, did they hop from roof to roof?

Did they ever show signs of violence while they were with you?

What is the function of this rod you failed to tell us about?

Mana’s tone becomes sadder as he presses the questions. He ponders how lonely it must have been for this construct to be assigned this station and then left to his own devices. Isolated in an attic with only tools to pass the time. Obviously the need for companionship was somehow instilled in him. Now even his tools were being taken from him. He begins thinking of a few questions for Valetta regarding the conditions Nim was expected to endure.

Maybe if we could learn Nim’s language and Valetta would excuse his service, we could adopt him and he could be taught to serve patrons of our establishment alongside Lif. Mana’s eyebrows lift as the thought crosses his mind.

Oriace folds his small hands over the rim of his drum and lets his deep voice roll out in an even, contemplative cadence.
“Master Nim,” he rumbles, tilting his head to catch the construct’s eye, “aside from the companion you wrought for yourself, have you seen—or sensed—any other nimblewrights moving through Waterdeep’s streets?” He turns slightly toward Valetta, letting the question broaden. “Is it possible more of your kind work in secret, beyond even your knowing?”

Nim gestures back that he doesn't know of any other Nimblewrights around. Nim hadn't named it, Nim believes it was possibly due to its construction why it fled as Nim wasn't certain what he was doing and it was more trial and error. Nim didn't see it hop between buildings, but it would be able to if it wished to. No signs of violence were shown. And the rod is a Nimblewright detector. Nim built it to track down the other nimblewright but discovered in the process that he couldn't leave the temple. 

Wagner speak aloud, "Perhaps we could borrow the detector, we aren't the only one's interested in finding this other nimblewright."

Hearing about the other nimblewright, Sterling's demeanor softened slightly. "We would promise to bring it back, of course," he added, "and it's not that you're in trouble. But we suspect things are going to get... out of hand if we don't find your creation, and quickly."

Mana crinkles his eyes and looks to Valetta with concern. “You said Nim cannot leave the temple. Is that by his choice or magical restriction?”

Nim’s whole treatment here sparks a faint recollection of a story somewhere deep in Mana’s mind, which he has no knowledge where he would have heard it. A story wherein a child wizard (was there a lightning bolt on his arm or head?) that was kept n a cubby under a stairwell and not treated very well by his guardians. He thinks the story went on to tell of great things he accomplished after he was removed from that guardianship. Whatever those tales of deeds were, Mana could not recall.

Valletta entrusts the detector over to you. "It is a magical restriction. It was put on both for his safety and the safety of others. If he was to wonder off he would quite easily get lost as his mind is not that different to a child. He is much smarter as is shown by his creations, but as for his mannerisms and behaviour that is where it is tricky. But yet he still is the size of a full grown man and so could accidentally hurt people without meaning to. It's why we keep him at the temple where he can experiment away, provided he doesn't hide things from us like a second nimblewright that is god knows where. As it sounds unstable, especially if it is the same one you mentioned to me downstairs, the House of Inspired Hands will pay you 500 dragons if you manage to destroy it and return with proof of destruction."

(think less Harry Potter, and more Lenny from of mice and men) 

Mana at first had been looking at Valetta. But as she spoke he shifted his gaze back to Nim. Her words sank in slowly. He kept looking at the construct for signs of emotion, of regret. He allowed his face to exaggerate signs from sadness escalating to surprised joy and yet nothing but stale metal stared back. There was no heart to reach, no soul to make merry. For a moment Mana thought this was the saddest thing he could imagine. Then he remembered there was another one of these on the loose, murdering people without conscious. Mana’s face fell. A truly horrifying quarry they were hunting. He turned back to Valetta.

”Did he create an off switch for his nimblewright?” Mana’s voice was much colder and his third person reference rang as if Nim was no longer in the room.

Nim is actually displaying signs of regret and sadness. It's less visible than in humanoids but he's not heartless (well, he is in the literal sense just not emotionally). "I don't believe there is such a switch for them. It is like a a body, damage it enough and the magic that imbues it leaves like a soul would leave the body."