I wonder if she revealed it because she felt like she needed to "come clean" to you before things go further, sort of like confessing to ease her conscious. It seems a strange thing to just randomly bring up.

What were you two talking about before this came up (IE how'd this topic come up?)? In what manner did she talk about it?

I don't think you have any reason to feel bad about how your feel. With the utmost respect to you and your girlfriend...her "record," so to speak, is a little on the extreme end of the spectrum, and I understand this is disheartening.

Give things some time, and allow yourself to digest the information fully before you act on anything. Why not talk to her about it? There has to be a reason she told you...you two might be in agreement more than you think on the matter.

I am sorry this has happened to you. I wish you my best.