How do I tell my "friend" that I don't want to take her to a concert anymore?

My dad got us tickets for a Lady Gaga concert a few months ago. Lately, she's been acting really rudely to me, and when she isn't being rude she's ignoring me. Sometimes she'll be nice to me, but I'm starting to feel like she's only being nice because she wants to go to the concert. I took her to a Muse concert and I totally regret it, and I don't want to regret this concert too. I've given her way too many chances, and I absolutely will not take her to the concert. How do I tell her without being too mean?