Yes, in my experience it is normal. I for one have never brought up my past relationships around my current ones. It’s just something I personally don’t believe is important to talk about. What’s in the past stays there in my opinion. I’ve always been capable of moving on. However, not everyone can do that, so when the topic is brought up, I believe it is important to be understanding because it seems like it took a toll on your current girlfriend. Relationships are important parts of everybody’s life, and they can take up a good chunk of a persons life. it’s hard to just forget about it in a short time especially if it was a toxic one. I have experienced what you are going through now. I would just lend her a ear and give her emotional support whenever she seems to vent to you about that past relationship, but also reassure her that she’s with you now, and maybe push her to move on from the past because she’s not in that relationship anymore, she’s with you and there are brighter things to look forward with one another.