It makes sense to feel upset and hurt. Has she been typically like this throughout your friendship? If not, could she be going through something? Has she had a change in her life that's made her more flakey? You have every right to express how it feels to you when she stands you up, and ask her "what's going on?" My only advice would be to speak in a civil way and not attack her, as much as you may want to, leave that for private thoughts, a journal, and writing here. Anyway, that's what I'd do.