Snarf, I wish I'd seen this topic sooner.

My experience is, if it didn't work before, then the likelihood is it won't work now. People do change sometimes, but not often.
And if she didn't appreciate how you felt about her before, then you're actually better off without her. And someone better will drift into your life, and make you feel complete, instead of like an unappreciated guy who's being jerked around.

I'm between relationships right now myself.
( I actually ended my last relationship in February. She was very beautiful, but increasingly smothering, jealous, and demanding of my time. Actually, neither of us were happy, and I was going to take her out to dinner for Valentine's Day, and treat her really nice, and then politely end it as friends a few days after the fact. But a few days before Valentines Day, she showed up at my door with all the stuff I'd loaned her, and she broke it off before I had a chance to. So although she broke up with me, I was actually relieved, it saved me the trouble. Although it was a pretty lonely Valentines Day. It would have been better to end it on a more positive note, with a last pleasant Valentine's Day together. )

I've gone out on a few dates over the last few months, but no real sparks with any of the new women in my life.

But a great lesson I've learned over the years is: there's one thing that's worse than being alone, and that's being with the wrong woman.

Trust me when I say that whatever you feel for this girl, she's fool's gold. No matter how you feel about her, she doesn't appreciate you, and she'd ultimately make you miserable.
So hold out for a girl who appreciates you. She's out there, just keep smiling, have fun meanwhile, and be yourself. And when you least expect it, you'll meet the woman you've been waiting for.

If she ever does call you up, play it cool, be friendly and go out with her, give her a chance. But again, don't put too much expectation into it working out for the long term.
Just enjoy going out with her for one night, if it comes to that, and take it one day at a time.
And again, if it doesn't work out, it's for the best, and there's better waiting for you down the road. Don't beat yourself up over what might have been, just keep looking, keep approaching women, and you'll find someone you really click with. Whether it's her or someone else.