When Is Enough Really Enough With Child Support

My husband has one child, she is almost 16. For 10 years now, he has been paying the $350.00 a month child support that he and his ex had agreed he would pay. He has never defaulted I might add. Lat year, we were married and he gets a letter that his support was being modified. It turns out, the ex had requested this. He now pays 550.00 a month, which still we don't mind, but the ex is still having the child ask for all of the extras she is wanting. For instance, money to have her hair and nails done, money for summer clothes, money for school clothes, money for the movies, money for a car, and to have her put on his car insurance also because she cannot afford it.

He has always carried health insurance also, and he will have to leave his job to take her to the dentist, doctors all because the ex feels that she will have to pay the copay up front. The ex is also remarried with another child, and uses that as an excuse. She can't afford to shop for 2 children. We did not argue the modification because we were led to believe that it was for health insurance purposes, only to find out later that the ex had asked for it because we married.
My husband does not talk to her, he just gives and gives just to keep from having to talk to her, but we are really struggling to make ends meat and he will sooner lose our house than for his daughter to think of him as a dead beat which her mom would say if he quits giving. When is it enough?