My 18 y/o stepdaughter feels entitled!?

My 18 y/o stepdaughter (just turned 18 3 weeks ago) is a total mess. We got full custody of my husband's 3 kids 1 year ago when mom tried to kill herself in front of them. We have done everything that we can for this girl. It has gone to the point that we have found marijuana in her room, she has come home blitzed and has also got herself in a situation to get ually molested. My question now is that she got a job at the beginning of 2011 and also gets $87 a month in a check from the SSA/Texas from her moms disability (because she is too sick to work and pay CS). Stepdaughter thinks that we should still pay for her lunch $ (even tho she doesn't have a lunch break and comes home and eats the whole house) and says that it is against the law for us to not supply her lunch money when we supply a roof, electricity, pay her cell phone, water, gas and all groceries. The $87 we were getting before she turned 18 was her lunch money. Help validate our decision??