My father has a PhD and always strongly advocated that school was our top priority. I am the youngest of 3 daughters - 2 of us have college degrees, the oldest does not. She was forced to go to college before she was emotionally ready and dropped out (and has not had the personal or external encouragement to complete her coursework).
I, on the other hand, had to spend my sophomore year out of college to earn money when finances were tight. I worked 3 jobs at 19 and paid for a good portion of college when returning. I chose not to get caught-up in the fun of being a 19 year old and saw how hard it was to have a good salary without a degree. It made me a much better, more dedicated student upon my return.
I share those stories because I think a lot of students are told they need to go to college before they're ready. We also asked our financial planner about a child who doesn't want to go to college - can 529 funds be used for trade schools (yes).
All you and her dad can do is to encourage her to make the decisions that will allow her to lead the best life possible. She may need to fall before she flourishes and learn through the school of hard knocks. I would recommend, though, not cutting her off completely if she chooses the option you don't support. Chances are, she'll learn quickly she made a mistake and will need your care and support.
I think one of the best life lessons my parents taught me was when that sister chose to get married at 19 to someone she'd only known a few months (he was a great guy, just not the right person for her) - when I asked why they were letting her, they said, "She's an adult, she can make her own mistakes. We'd rather let her make a mistake and be there to support her than to lose a daughter". All of my most important life lessons have been learned by persevering through tough times.
Good luck. It's a tough situation.