A player of mine has an idea of using invisiblilty on another player in her group and then beast shaping into a small insect or rat or scorpion sized thing that will fit in there pocket. In essence there trying to get around having to use 2 spell slots of invisibility to make the Druid invisible as well and want the fact that it makes your clothes invisible as well as a reason that since she’s in there pocket she is also unseen. Is this something you would allow or should I allow it?

I would allow it.  However, since invisibility is a concentration based spell, the druid character would have to avoid damage, or make constitution provided the damage in itself didn't revert the druid back to natural form, and avoid casting any other spells while doing this one.  Very creative.  I like it and would encourage it as a DM.

Yeah, seems to fit within the rules. Kind of cheesy (no pun intended), but works.

If it becomes annoying, have the druid overstay her wild shape time limit (especially if they are low level). A druid can only stay in wild shape up to their level in hours... While they're trying to wait for an audience for the king, let them have to wait a few hours then BOOM. Exploding pockets of druid appear busting their scheme.

(granted, this won't happen often especially if you've done it before).

If they're both abusing it then just take them to the side and tell them to cool it but overall, until level 20 a druid only has 2 shifts per short rests while their spell slots increase every level, especially if they're a moon druid they're going to want their shifts for combat as often as possible.. and at level 10 it's going to take both uses to turn into an elemental.

So halving or completely nullifying their combat usage for a level 2 slot is more of a sacrifice then the cheese.

If she's not a moon druid introduce more scouting or tiny spaces or other scenarios where the party specifically needs either a tiny or larger animal where the cost of a level 2 spell slot may be worth less than the wild shape usage. 

Remember they replenish 2 per short rest too. I don't want to say to cut back on their short rests especially if there is a warlock, monk or another class who needs SRs but it is an option too. 

Something to consider: the spell is an Illusion, it only makes people think you are not there. The spell only blocks you and objects you wear/carry from their minds, so it is entirely possible they'll just see the floating animal.

However, without invisibility the druid still gets total cover being in a pocket too, effectively making them invisible anyway, so I'd allow it.