It's up to her to decide if she can get over it. Honestly if she can only be with someone who has no past relationships, then she needs to find someone who fits that requirement.
This is key. The concern is hers. And the choice of how she will deal with it is hers. The only healthy thing you can do is let her make her choice whether to be in this relationship.
And remember that her feelings are hers, and they are very real. She really is upset/angry/jealous/etc. You have no power or ability to change her feelings. You can't even manage her feelings for her, although you may be able to help some. Trying to manage her feelings is a horrible codependent quagmire for you to get stuck in if you try.
Since you cannot change your past, you have to let her make her choice. Besides that, there are a few things you can do to help or make things easier for her/better for your relationship.
1. If these fights become verbally or physically violent and toxic, removing yourself from her presence temporarily is better than staying "calm" while she rages at you. And when I say better, I mean it is healthier for both of you, not just easier for you.
2. I'm assuming you don't bring up your exes with her, or not intentionally. If you do, stop it.
3. If you have stayed on good terms with any of your exes, and are acquaintances, or even friends, you can reconsider. Think about it before you shut somebody important out of your life. One of the bad behaviors associated with BPD is isolating you from friends and family, and many members have regretted allowing that to happen to them. That said, exes are a special case, and I'd give in on that more readily.
4. You can validate their feelings, like being upset, jealous, fearful, or whatever is expressed.