Which feat to choose for my arcane trickster melee charging rogue?

Hi, friends!

I have to choose a new feat for my Arcane Trickster Rogue, and I can choose a feat from either 5e or 5.5e. I desperately need help choosing. 

The feats she already has: 

• Charger (+10 Speed when Dashing. Charge Attack: Run 10 ft in straight line and add 1d8 extra damage to Melee attack)
• Fey-Touched (New spells: Misty Step and Hunter's Mark)
• Piercer (Reroll piercing damage roll once per turn. Add one piercing dam die when critting.)

Some background: Her signature fighting style is charging ahead in combat for extra damage with her rapier casting Green-Flame Blade for extra fire damage and disengage to get out of reach. She does not have a high health pool, at 67hp. She's now level 12. She's got 20 in dex and 19 in Intelligence, which means that preferably I would like to get an increase in int. 

The feats I am considering:

• Shadow Touched (5.5e) Intelligence: +1. New spells; False Life and Invisibility. This will help me as a front fight charger, in terms of hp and an added elemental of magical surprise.
• Elemental Adept (5.5e) Intelligence: +1. Ignore Fire dam resistances and treat every fire dam roll of 1 as a 2. Will help my spellcasting and my Green Flame Blade attacks (as well as Firebolt) which I use all the time as part of my normal melee attacks.
• Mobile (5e) Speed increase 10 ft. Difficult terrain cost no extra speed while dashing. No provoking opportunity attacks when making a melee attack. This helps my playstyle immensely, by being able to fly in - attack - and fly out again without having to use my bonus action on disengage! But I wont get an increase in Int.

Thoughts anyone?

My initial thought is that Mobile would be a really good feat for this character, and the opportunity attack immunity alone is going to be worth way more than a +1 to Intelligence, especially when your Intelligence is already very high for an Arcane Trickster at that level. It will mean that a lot more of the time, you'll have a bonus action free to do stuff other than Disengage.

If you find yourself very often casting spells that actually use the spellcasting ability, that extra +1 to Intelligence might be worth it. But most Arcane Tricksters don't ever push their Intelligence that high, and prefer stick to spells that don't use it.

I dont know your Attributes or Saving Throws but its a rouge :). So maybe the Feat Mage Slayer is worth a look, just to have a fail save against nasty spells. But Mobile is a great pick, too.

If you really want a +1 Int Feat i would take a look at Telephatic. IMHO the Telepatic Utterance gives your Character more utility out of combat, but not sure how much this is needed in your case.

Another vote for Mobile, but why not take Speedy (the 5.5 version of Mobile) and bump your CON by 1? And all Opportunity Attacks have Disadvantage, not just from your target.

Mobile is for hand to hand back stabbing.

Use a ranged weapon or spell, your a caster.

Fay touched

Elemental adept

Ritual caster from 2014 or Mobile

But I like spells and range more than melee

Some other good picks that you might want to look at that nobody has mentioned:

Elven Accuracy  - Amazing for a Rogue if you are an Elf of some kind, especially on a Rogue, can increase Int

Fairy Trickster - Fitting for an Arcane Trickster; won't increase Int, but will make it easier to land your Cunning Strike options (My personal favorite)

Lucky - Amazing on a Rogue for on-demand Advantage when you don't already have it;  no Int boost since it's an Origin feat

Tough - An extra 24 hit points at level 12, with 2 more each level; another Origin feat, so no Int increase.

How about telekinesis. Your mage hand is invisible but gains 30' range so as an arcane trickster you can pick pockets, open locks etc from 60' away - plausable deniability as an alibi every time. And if you ever (like as if I know) have a BA available you can shove someone. Very useful to move allies out of grapples etc as well as moving enemies. And you get that +1 INT.

How about 5.5 War Caster? You get the +1 to Int, can cast Green-Flame Blade as an Opportunity Attack, have advantage on some Constitution checks, and can cast spells with your hands full.

Edit: Green-Flame Blade doesn't qualify, since it can target a second opponent. Maybe change from Green-Flame to Booming Blade? Don't forget that if you meet the Sneak Attack requirements, you can get your Sneak Attack on an Opportunity Attack, even if you got it on your last turn.

Ability Score Increase. Increase your Intelligence, Wisdom, or Charisma score by 1, to a maximum of 20.

Concentration. You have Advantage on Constitution saving throws that you make to maintain Concentration.

Reactive Spell. When a creature provokes an Opportunity Attack from you by leaving your reach, you can take a Reaction to cast a spell at the creature rather than making an Opportunity Attack. The spell must have a casting time of one action and must target only that creature.

Somatic Components. You can perform the Somatic components of spells even when you have weapons or a Shield in one or both hands.

I feel like the answer is always 2024 defensive duelist. As a reaction if holding a finese weapoon you can perry a melee attack adding your proficency bonus to your ac on any hit until the start of your next turn. You also get to add a plus one dex stat bonus which you sadly do not need. But this is a plus 4 AC Bump(basically a shiled spell every round at level 12, plus 5 at level 16 and eventually plus 6 at level 17) against any melee attack.

The answer is always defensive duelist if you weild a finese weapon.