She's immature and needs to grow up. If she would spend her social media time studying Dave Ramsey's money techniques, she could turn things around. There are several Facebook groups (one on Baby Steps) that have discussions about money. Get her to join the groups and read. Actually, have her post your situation there and ask them what she should do. (Then stand back.)How can approach this?
In the end, there's probably nothing you can do. It's worth trying, but don't spend the rest of your life doing it. Don't have kids with her.