In need of helpful advice on dilemia with close friend?

I had a friend, whom I was got back in contact with, is acting really funky lately and I don't know why, she would call me, and invite me places, and chit chat with me, but recently, she has struck up more of a close friendship with a mutual friend that I introduced her too, I came back to visit,we went out to dinner, she wouldn;'t give much eye contact, and when we were meeting up, she was calling my mutual friend Tania, I introduced her too, and not me,she just wasnt engaging at all, ,all she kept saying the entire night was you make me goofy, when I see you, and was just randomly laughing for no reason, which I found to be sort of disrespectful, and later on that night she asked me to take my shirt off, she kept calling me a nerd, and kept saying she cant picture me having at all,and she goes off into these conversations everytime we hang out, and while I was sitting there,she handed Tania her phone to look at her pictures had to ask her can I see them too..me and my mutual friend, planned to go to her sister baby shower, and I asked her for the address, and what did her sister want, and stuff, just trying to make conversation, and all she could ask me was.."Oh is Tania coming ?and asked me " Is she working" and ever since then she will not invite me anywhere, she will only invite my mutual friend Tania,Tania is telling me she invites her to go out to parties, over a celebrity rap star house to have lunch, she went over Tania house to hang out a few times, and she never askes if I will come along,its very weird, and I don;t know why? and since then I havent heard from her in over a month, she refuses to call me, or text me, or email me, and I don't know why? Any explanationas to why someone would suddenly just stop talking to you.