to be honest, her getting with someone who sounds like it IS a coping strategy. everyone i know who's ever done that did that bc they were uncomfortable with the idea of being single. so don't look at that and go "why can't i get over it that fast", because no one gets over relationships that fast, healthily
just take it slow. you'll be okay eventually. it took me a year to get over my last relationship (partially bc it was abusive), and i still have moments when i'm upset thinking about it. but eventually you'll realize you don't think about it that much, and you can be happy on your own

on her being with someone else already. Says a lot about her.