Well, you know, look how often you HAVE been there for her while she was growing up. She graduated college, so, you did a lot of somethings right.
How many times did she let YOU down when she was a teen? I know, it's part of growing up... But seriously? People will let her down throughout HER life too, and sure, it's a rude awakening, but, this is a good lesson for her to learn, because it's something she will have to get used to as life goes on.
It's not like you forgot, or purposefully skipped out on her. You're having car troubles, and in this economy, difficult to fix. When she realizes that you couldn't have made the trip w/o risking your own safety, she will understand. She may not forgive you now, but, she will come around.
Your daughter is beautiful. :) Congrats on a great job raising her successfully into adulthood!