She would have to approve of you turning your joint bank account into your own account. I assume it was created when you were legally a minor, so chances are pretty good that it's a Mom and then kid type of thing.

As for the app, it's a family plan phone (verizon, att, sprint, etc), despite giving your folks money, it's whoever's name is on the phone. If it's your mom, it's technically hers.

I wonder if this is a "I don't really feel like getting yelled at" or will your mom actually go nuclear on you for wanting to spread your wings a bit? She's not going to have much control over you at college anyway, if she's footing the bill, that's about as far as it goes, she can't see your grades or anything. FERPA laws prohibit her.

May just need to actually talk to her about things.