What is the reason a girl who didnt like me, now want to hang out because she found out about my friend?

I really dont think she likes my friend who is a girl but we (me and my best-friend who is a girl and BEAUTIFUL) at a ice cream shop having ice-cream and this girl (Cindy) i know, i ended up asking her out and she said HELL NO. Well she walked in and saw us sitting down. She came over and said hello, i'm staring at her weird like WTF? She goes oh i didnt know you knew Amanda (my best-friend) I was like umm yeah i known each other for 10 years. She goes oh ok and walked off. My best-friend said i dont like that girl! I asked why, she said because they almost had a fight in high school. So me and my friends and Amanda friends (4 guys and 9 girls) are planning a VEGAS trip next sunday for one of Amanda friends birthday and she (the girl who turned me down and we haven't spoken in 6-months) calls me saying umm i heard you and Amanda and friends are going to vegas? I like umm yeah how did you get my number? She said from a friend and she wants to come. I was like umm sure, you can ride with Amanda. She said i really want to hang out with you in vegas, we can do this and we can do that? I'm confused on why all of a sudden she wants to hang out?