That's a tough one. While you can't make someone like you that way there are things you can do or not do to kinda nudge it in your favor.
Pestering her about it is a bad idea. Nothing is a bigger turnoff than when a guy pisses and moans about "nobody wants me boo hoo why don't you like me?" Just play it cool.. Be nice to her and give her space. This can possibly make her miss you.. Giving her compliments is fine but if you do it constantly she will just get a big head. Go a day or two without talking to her much or complimenting her, since y'all had a thing before, this might plant a little seed of doubt in her head and she will wonder why you haven't stroked her ego that day. Sounds cruel when I word it so frankly but really it's harmless. The old adage goes "absence makes the heart grow fonder"
Just don't overdo this or be an outright dick to her or it will backfire. And remember that there is no guarantee this will work. Do you always talk to her first?