Well I recently learned that she asked if I asked anyone out to the prom yet but she knew I didn't go I found info saying if a girl does that she wants to go with you so should I ask her out again?

Chances are she was asking around as she was hoping you would ask her however, if you asked he once and she already said no she could be asking just to see who you are going with instead because she was going with someone else and that fell through. It would depend on your situation but if you already asked and she said no I would not ask her again don't take second best ask someone who would appreciate being your date and that you would have fun going with.