Best friend lied

So my best friend and me dislike this girl (she lied about being pregnant when I was going through a miscarriage and lied about her child having a disease when there was no child) however the other day my friend decided to go and visit this girl and hang out at her house...its nearly impossible for me to get my friend to come over to mine. My friend sits and bad mouths this girl All the time yet she still goes and sees her and chats to her. It's really hurt my feelings because I feel as though I have been betrayed by her.