Years ago i was actually in a relationship with a guy who just lied about everything!!! unfortunately i didn't realise till we had been together for three years! basically he was so incredibly insecure about himself and tried to create a life that people would find interesting that he spun this huge web of lies and stories and it all fell apart cause he was sending him self mental (and i don't mean figuratively speaking) . i felt really sorry for him, but that was the end of the relationship. i think it says alot about your friend, she obviously feels the need to lie for some reason.
i dont know how you could deal with it, once she knows you know she lies alot she could be really embarrassed and that would affect your friendship, or it could be a huge relief for her!?
good luck