Great job!!! I know that must be heart breaking to deliver that news.
I would calmly explain to dear dad that if he's not willing to help with educational costs that if he is declaring her as an adult dependent id ask him to remover her as his dependent on his taxes. Let her fill out a FAFSA form that is not tied to his earnings and your little girl may get a shot at going away to school.
It's a dame shame when a parent uses their child's future and education as a chess move.
You did the right thing I bet your daughters are very proud to have their mom emotionally there for them when they need it.