Friend betrayals at work?

i worked with some of these people for a number of years. One of the girls got fired for falsifying work information. She was also quite the backstabber and was very sweet when she wanted something and then when she didn't need you anymore then she was done with you. I heard that another friend from this office and her were in friendly communication. I asked her how she could ociate with someone that behaved that way and treated people like that. She told me that it had nothing to do with her because she felt that this person never betrayed her. So my question is...as long as someone doesn't screw you over but you know they have screwed your friends over would you have anything to do with them. I wouldn't ociate with someone that treated my friends that way.