People can still think of others before themselves - but that could include the OP and her DD, too.
Many people are assuming that the OP's version of events is the only possible and correct one, whereas others having been saying that really there are loads of interpretations of what went on, that it was not necessarily a deliberate, mean act on anyone's part, that anyone was necessarily being dishonest or selfish or not showing integrity. We only know OP's version of it. Her DD might be the sort of person that is difficult to be around, doesn't pick up social cues, changes the whole atmosphere at a party, even if they don't mind be friendly to her on other occasions. Or maybe not. We don't know. We don't know that she was the absolutely only one not invited to something and everyone else in the room discussing it was, or that everyone knew that, or that everyone even considered her a friend who might have been invited - they might well have just thought of themselves as a group of school friends, and barely considered the DD as anything to do with that group. Who knows. The girls/mum might have responded with what seemed like 'warmth' but really there were social cues to show that it was just an act, and it would have been uncomfortable for the DD to go where she wasn't wanted in the end, but neither OP or her DD picked up on those. Again, we don't really know.
It sounds like it could have been handled better from the moment the DD invited herself along, to the time that it was cancelled on her, and how it was done, for sure. But so much else is just assumption - it might be correct, it might not be, but why not just go for the best assumption, which is that the others don't specially consider her a friend, rather than deliberate meanness. But the OP's version of events is simply that, one version, and I think many people who are saying "it's not mean" are actually saying "it might not be mean because that version of events might not have been what happened from the other person's perspective".
Maybe they don't really like the DD all that much, but parents have up til now tended to organise lifts or activities. People would also get upset if the others kept rejecting any lifts or activities or parties or invitations, because they didn't want to become specially close friends with the DD - and she might end up totally isolated then. I think you have to decide whether to extend an invitation based on what you want at the time, and not on whether someone is going to reciprocate later on. Maybe they will, and it's a chance to get to know someone further so that they might decide to reciprocate. But I think I'd be more hurt if people rejected all my invitations from the off because they didn't want to become close friends. I might eventually pull back and stop inviting them so much over time ,or I might just accept that they have lots of friends and I don't, so I am in the position of having to work harder to have a social life, and if I want to do anything, then I might still invite them, reciprocated or not. I think the DD has that choice now - start to pull back from these girls as she's not part of the group in the way she thought she might have been, or choose to stay friendly but not close. Neither is the wrong decision.