I agree dead on with the whole you are financing this behavior.
Explain to her you saw what you did. And that this is not what you are paying for. Give her a months notice she is on her own. She needs to have a job and pay a percentage of what you deem as reasonable.
Reasonable in the real world. Not mommy and daddy love baby world. Hold her accountable for her own.
My daughter is 19. She has been in some real sh*t. Though, I think we are turning the titanic around, slowly. very slowly.
It is through accountability. She pays for half of everything.
She works overnight 10 p- 7am. Then goes to school 12:30-5pm . So what little free time she has, she is pretty worn out. I think it keeps her out of most trouble. But she still manages to be ridiculous some.
I had to stand my ground pretty hard, however. I told her flat out. You want your own life to do your own way, then get out and go pay for it yourself. I am not helping in anyway. I backed that up with action.
As time has gone by and she stays out of trouble, I have been able to soften a bit. I am very cautious, however, to always withdraw that if she begins to get out of line again.
I have seen some pics on facebook to that I insisted my daughter remove or lose access to the computer that I bought. I explained the whole rest of your life thing. she doesn't get it,nor does she care at this point.
I really think an intervention/confrontation thing is out of line because she is age of majority. Besides which, she is going to fight you tooth and nail. I think it is a control issue. You need to let go of mommy control and let her suffer the consequences of the real world way. Pay your own way, girlfriend.