There is a forum for people who's partners have personality disorders:
http://forums.psychcentral.com/forumdisplay.php?f=132
(sorry if you keep getting redirected).

Unfortunately I can't offer any advice on how to be with a partner with this disorder. I can only speak from the perspective of HAVING it. I think the best thing you can do is be supportive (she can always come and talk and hang out with us here), if she knows you support her and her recovery that is a great start.

I would browse online (as well as talking with other people who's partners have BPD) and read more about the disorder. Education and knowledge is SO helpful.