That your "friend" initially agreed to drop you off, but later backed out, suggests an unreliable nature to put it diplomaticly. That she did this on the occasion of your birthday weekend, and considering that you had been able to secure a considerable discount for her and the others, also suggests an ungrateful spirit. I wonder if up to this point she had been a quality friend or has she ever displayed any inkling of this type of nature before.

In any event, you could look at it from a positive angle and say that she has revealed a side to her personality that it's better to find out about sooner, rather then later. If you are the kind of friend that is loyal and willing to go the extra mile for a friend, then you should be able to expect the same in return. If it's not forthcoming, then maybe it's not a friendship worth continuing unless you are willing to give more then you receive in return.