She cannot do a whole lot without your support especially if she financially dependent on you. Even if she is to get a job, does she think that they money she will be getting will be enough for her to live sufficiently and independently? Let her do some research as far as what each job pays, what experience and education she has to have, how much does it cost to maintain a living from having a car, apartment and all living expenses covered.
If only has a year or so left to finish school, it may be best that she finishes what she had started. Point out to her that otherwise it is wasting resources and effort.
You may suggest to her to speak to a career counselor at her current school. They can help her with objective feedback if she does not believe what you're telling her. You could also present it to her that she could speak to a counselor elsewhere because it does not seem that her plan is a workable one. That she has to look at whether the information is coming from you or someone else.
If she relies on you for her car, cell phone, money, etc. you can limit her to only the most essential- food at home, shelter, etc. All other "extras" if you're paying for them ought to be taken away and earned by her even if you use them as a reward for going to and finishing her school..