its like smudge said "a friend in need, is a friend indeed"
some people want to be your 'friend indeed' when they can get something out of it - they will suddenly start acting like your the best person in the world just before they ask you for help, then as soon as you have helped, they go back to just treating you as usual.
has this woman been a good friend otherwise?
though, at the moment, i'd give her a bit more time - she is probably feeling a bit spaced out and perhaps it hasn't occurred to her that you all may be feeling put out.
once she gets her head round whats happened, she may do something for you.
i do know how you feel though - i once took a girl to hospital - she wasn't an especially good friend - because she got herself into a flap thinking she'd been stung by a wasp and would have an anaphylactic shock (!) - she had actually just pricked her finger on a sharp piece of nylon thread in her sports bag...but i paid for the cab, the tea, the cab back - and i missed my college performance assesment because of it! ... and i got no thank you, no payment for the cab and no drink - our tutor bought me a drink - on her behalf - for looking after her while they did the production!
i even got a few strange looks from her mum and dad who had been called ...??!!
it really annoyed me - because she wasn't a friend, and there was nothing wrong with her - i suspect it was deliberate because she too scared to go on stage...!