Your signature says "Life is too short to be spent dwelling on the past" so... don't!!
Just act normal! Don't be a jerk, talk to her when she talks to you. Don't be put off if she doesnt fall all over you or anything. Don't worry about her, she's being a silly little girl. But no offence, you're being a bit of a silly little boy too
Just act normal towards her, don't make any efforts or anything. Soon things will even out.