Why Does She Do This?

So my friend and I have been bff's for about a year now. We are close as can be, and she always looks for me at lunch, break, etc. We always have a lot of sleepovers and stuff, and we always bake cakes for each other on our birthdays. Basically, I know she's geniune. However, she does this thing sometimes which I don't understand. Most recently, we got our schedules for the school year; I had no cles with her. Desperate to change, I smoozed the head of high school to let me into one cl with her, which was fine. However, she was telling me how bad one of her cles are, and I realized she could switch with another so we had two cles together. I pointed this out, and she said I was right, but after the weekend I came back and nothing changed. I asked her about it again after she complained more, and she had a mixed response. Then at lunch, she told everyone I was "trying to convince her to join" not in a mean way but as part of a joke. The cles are the same at my school so it's not like she didn't want to take the cl. I'm baffled why she did that.Why does she act like she's sad she has almost no classes with me, yet does this thing? Another time I offered to go to a party with her, again a denial. When she learned I hadn't gone after all, she kinda smiled to herself. I mean, what's with the random power play? It saddens me because in the past I was sick and she was the first person to notice and took me to the office herself, not caring that I might give her germs. Weird thing is, she doesn't have many friends so I know she's not pulling away. Is she, maybe...a little bipolar? Thoughts, please!