has always been like that when it comes to too much time around others and needs to 'recharge'.

That's classic introversion. Period.

If she recharges solo, and in proportion to the level of output required in interactions with others... yup.

{raises hand}

Even with my own family, after a road trip, I have to retreat into my own space for a while. Headphones and music are a lovely thing that way. Might be something to try.

Schrödinger's cat walks into a bar. And doesn't.