Since she offered to take you home to were your car was , I don't think she was terribly rude (her mom didn't ride with you to event, correct mom came on her own after?) She ofter to "make you whole" /put you in the same situation you would have been in if you didn't ride with her albeit a few minutes later.
POD, this is what I was thinking. My interpretation was that when her mom showed up unexpectedly, Melissa could no longer go with you to the party as planned, but offered to do what she could
, which was to take you back home, and then you could've driven yourself to the party in your own car. I think Melissa should definitely have apologized for the change in plans, but it's not like she left you high and dry--in fact I think you kind of let her off the hook a little when you declined her offer to drive you back home.
A lot depends on tone/attitude. If she was like, "Whatever, gotta go, you'll manage, right? You didn't want me to drive you home, did you?" I would be pretty mad about that. "Uh, YEAH, if you're no longer going to the party with me, at least take me back home first!" (that's what I'd be thinking anyway). Ideally she would be more like, "I'm so sorry, this is very unexpected, but I have to cancel on going to the party. Can I take you back home?"
I could be misinterpreting the chain of events, though.