My "best friend" is a total *****...?

So recently my best friend of 2 years? i think now has been.. well, changing, becoming more bitchy and like the common hoes in my school. She's still cool to hang out with sometimes but she doesn't seem to give a **** about me anymore. She even said (when I tried to talk to her about this guy I like) "whatever, i dont give a shite anymore!!" I even talked to her cousin who agrees with me about her changing, and she's becoming more vain and shallow.. she's 13 and I'm 14 so I know it's a time when people change and I'm really trying to put an effort into the friendship but she's not so why should I? Also I've gone on holiday about a week ago and she didn't even bother to text me or ask on Facebook how I am. I have another friend, this one is actually really great though. Her name is Cindy and she's really caring and funny, and I know she's actually what a best friend is suosed to be! We're almost like sisters. But all my "best friend" (lets call her Lisa) does to keep our friendship is say that she's my best friend. I know I should probably talk to her about this or focus more on my friendshi with Cindy or others but Lisa isn't a good person to talk to about stuff like that. If I confronted her about it she'd just get offended and start an argument. And I'm way too nice lol to just say "yeah we ain't bffs anymore" so.. :P if there was a gentle way of sorting this out, I'd really appreciate you guys letting me know :) Thanks in advance :D