R..
I don't know if I am repeating here... BUT...
I would say she pays for all her entertainment like you have her doing. I would also have her pay like 1/2 her phone bill.
I would ALSO charge her about $50 a month (or maybe $100 if it will leave her enough left over...) in rent. BUT instead of keeping her rent money, put it in a college fund for her.
When I was 16, my dad was struggling to raise 4 kids on his own without child support from my mom. When I started working, I started paying ALL of my own bills, about 1/3 of the household bills, and clothes for my siblings. I definitely don't think it's too much to ask for her to contribute a little bit.