I agree with Chicken Lady, I'd pay dental costs if it wasn't a hardship for me. But you know what I thought of before the OP's last post? Birth control. I'd pay for really excellent, super-duper extra fine birth control first, before dental work. Preferably the kind of birth control where it is stuck in her arm and she doesn't have to think about it for months or years.
But the rest of it--nope. Although if she is only borrowing money, and it seldom happens, and she is reliable about paying it back, I'd lend it if it was an amount I could easily lose.