My bff's old bff doesn't like me what should i do?

okay so, me and my friend Katelyn (who i was friends with in highschool but wasn't really that close to) became closer for the past year, so now i consider her my bff, and we hang out all the time, take loads of pics etc. Now Katelyn's old bff Melanie thinks that i'm "trying to tear their friendship apart". The reason why i know this is because yesterday i asked Katelyn what she was doing and she said "ohh, im going to the movies with Melanie" so i asked to come, and she said sure. (me and Melanie are friends.. but for some reason i feel that she never liked me) and like right after i asked to hang out she tweets on twitter "I hate it when people invite themselves". Like at first i let it go, cause i'm like okay, theres no way that that's about me even though it was OBVIOUS since we were hanging out that day :S. i checked her twitter again today and she tweeted "She's living a sad life", "You are now considered my enemy >=[", "This ***** is trying so hard to pull us apart. Not to worry, we got years together more than you 'll ever get.", "Being the centre of attention is all you'll ever be #*****", "*is all you'll ever GET to be"... yeah, pretty obvious. well the whole time we were hanging out, she made it seem like she liked me so i don't even know...i wanted to talk to her about it.. or should i just leave it alone?