Bro, she is doing one of two things
1.She has you in the pic to create drama/make her bf jealous.
2. She likes you, but she isn't going to let her ex go until she finds out if you are a step up for her on the food chain. As I look back at all my relationships when I was younger almost every girl I went out with had an ex she wanted to break up with, "just broke up" (lie), crazy ex stalker (meaning she was still fucking her)
You see...Girls are like Monkeys....(I have posted this before)
Girls swing from branch to branch. (guy to guy) However, they won't let go of the current branch until they have a good hold of the new branch. And, made sure its a strong enough branch before they swing over. If not...Well, they just swing right back to the first branch.