She's in her twenties? This entire time I assumed Mia was fourteen, or thereabouts. She does not look like someone who has reached her adult height, at the very least.
Do these gems happen to… y'know, glow a lovely soft blue under the moonlight? Or a wonderfully ethereal green? And they're always slightly warm to the touch?
Can put anything she can see, including living creatures, into her storage space without restriction or limit, where no time passes for them until she takes them out again.
… if that's not an instant-kill ability I don't know what is. If you never intend to withdraw someone you effectively erase...
If it's anything like the setup my parents used; they have a main account for expenses, the contents of which are spent via mutual agreement – and then each of them gets an "allowance" to spend on whatever frivolities they want.
It keeps one spouse from blowing the account on expensive hobbies...
Looks like the little girl has relied too heavily on Rule Zero and thus run afoul of Rule -1:
If the players are no longer willing to put up with the GM's invocations/abuse of Rule Zero, they stop playing the game.
Dangit gal, the correct thing to do in this scenario is to pull a Solomon and wish for the wisdom to use your power effectively and well. Or at least wish for a more manageable activation method than “touch thy thighs”.
In this particular case, our protagonist is considering concealing their power because it's rare and valuable and people are unscrupulous. After being told Noct gets kidnapped on the regular because people want his healing magic, apprehension is probably the healthy reaction here.