My friend is being obnoxious?

Ok so i've been really busy the last few days and haven't really had much time to hang out. My friend has been trying to get me to go shopping with her, but I keep having to say no because I'm busy. Two days ago I told her we could go the next day and she just said "whatever bye" and hung up, so I took that as a no. Then my other friend came over the next day and asked if she could sleepover so I said yes. My first friend called and asked If I wanted to go, but I couldn't because of the sleepover. So then today she called me a few times (I wasn't at home, I checked my voice messages) and I called her back and said I'm perfectly up to going today. Then she said (in a VERY cheerful voice) oh! i can't I have plans, sorry (she didn't really sound sorry) "maybe another day?". I personally think that's her bullshit excuse meant to make me feel rejected. Do you think she really was busy or just saying it?