If you’re otherwise happy with this girl, I don’t think you should break up with her over a reason this shallow. She didn’t do anything wrong. Who cares about what she did before you met? Really ask yourself if you’re going to end an otherwise healthy relationship over things that happened in the past and didn’t involve you whatsoever.

Are you still in therapy? I would mention this jealousy to your therapist. They may be able to help you work through it in a healthy way.

If you really can’t move past this for whatever reason, then break up with her for HER sake. But my advice is to let this one go. It doesn’t have to ruin your relationship if you don’t let it.