What's going on? Why is she cancelling on me...?

There's this girl i like, we've known each other for 3 months. The first time we were supposed to see a movie, she ditched because her mom made her go to her brother's award ceremony...She actually did, so i didn't think much of it...we went the next week. Well, a month later, she asks to hang out, the day comes, I text her asking if she'd like to see a movie, and she says that she just saw it last night, and she has to go bathing suit shopping with her sister, so can't come. I really like her, we're married on facebook, send hearts via text, talk everyday usually (except for 1 week, when she was VERY distant and weird) she calls me, and we have pet names for eachother. What gives? why is she canceling on me...Does she not want to see me? Sometimes she doesn't even respond to texts...but when she does, shes amazingly cute and nice and sends hearts and petnames. Does she like someone else?