Absolutely unfair IMO, you are considered an adult at 18, of course it does depend on each individual doesn't it?, but you sure sound mature enough to me,i guess if it really is bothersome you should shift in to your own place and get your independence.

However i agree with K & L too, you are under her roof, paying no board, then i guess you just have to go with the flow and live by her rules or move out.,your call, if you really want the independence then it is time to move on.