&gt;Which I really don’t understand, because you don’t get angry unless you care right? You don’t get angry and get upset just because of something/someone that you don’t care about

Dude... she's 18. She hasn't *lived* long enough to put some hurts behind her yet. Sure, it's maybe unwise to continually bring up exes, but again... she's 18. She probably doesn't have a large relationship toolkit to handle things the right way 100% of the time.  She's got limited life and relationship experience to draw on. If the ex stuff really bothers you that much, maybe say something along the lines of...

*"Hey... so I'm really happy that things are going well between us, and I really appreciate that you're vocal about letting me know when I'm making you happy. I wouldn't want that to stop. When you bring up your exes all of the time though, it kind of interjects them and your old relationships into moments that should just be about us. Do you think maybe, as bad as they turned out for you, that you could let them go a bit and just be present in the moment with me?"*

That gets the point across in a healthy and productive way without making her feel too bad.