What to do with this friend?

Last year I became friends with a girl who joined my circle of friends. This year we didn't have any classes together, but we still talked. Whenever I try to make plans with her she always is either not able to make it or cancels last minute. I would normally take that as a sign that she doesn't want to hang out except that she will try to reschedule our plans for another day though it never works out then either. I'm really confused because in person she is really nice and cool, and she hangs out with other people. Is it really never working out, or does she not want to hang out?