Oh, my. Leann's right, don't make somebody a priority who makes you an option. Please, please don't cave and please, please don't continue to explain yourself or your decision to her because it's just not necessary. You're entitled to decide what you want to do with your life. You told her it's a no-go and then told her to give you time? That sure sounds like a mixed message to me! If I were a love-struck high school girl mooning over a crush and he told me to give him time what I'd hear is that there's hope.
It's flattering to be so wanted that she'd phone, text, email, drive for 2 1/2 hours to see you after you've told her it's over and done with. Do you really want that kind of attention from somebody you no longer want in your life? That borders on stalking, for heaven's sake!
Sounds like you've been as patient as a saint, as kind as possible, and gracious as well. Maybe it's time to stop being gentle but firm and start being cold and deliberate because so far she apparently hasn't paid attention.
And still she insists that you get back together because that's what SHE wants?There's a way to put a stop to it and make it stick: employ the blocking feature on your phone and on your computer.