But it is different because they are adults. You can put on a friendly face around someone you don't particularly get along with or want around you for a few hours.
Children can't do this. At my daughters 12th birthday party last week I couldn't believe how much bickering there was around a group of 8 girls.
I'm not saying this is the case but what I would suspect is that the other child could of been worried that your dds presence could of caused something different to what they had planned. I'm not putting your daughter down here at all. She seems to have handled the situation well by what you've said.
It's just something I've seen with my dds. Quite often I've found that groups of girls exclude others. There's always a reason behind it, most of the time its petty. My daughter once didn't get invited to something because she was the only one that didn't have Tik Tok. Ridiculous but equally i wouldn't of wanted my daughter there if she's not welcome. I don't think it's fair on anyone.
The majority of kids will feel left out at some point. Wether it's not being invited to something or having no one to play with at school to being the only one that doesn't have a phone or the latest pair of trainers. It's happens to us all and it's part of growing up.
I don't think anyone can be pin pointed as being to blame.
Fair play to your dd for having the guts to do it but she shouldn't of asked.
The mother shouldn't of really said yes but equally I don't think she would of done if she knew it was going to be a problem. I imagine her trying to convince her own dd but her dd was having none of it. She was wrong to leave it so long to text but equally she could of spent the last few hours trying to sort it with her own dd. Who knows? Unless I've missed that part. But I bet that wasn't an easy text for her to send. What else could she say other than the truth? An excuse wouldn't cover it. She was maybe equally miffed to be taken off guard. Also sleepovers with a bunch of pre teens is stressful! She's probably stressed out now to the absolute max before the sleepover had even started.
Her dd could of been influenced by her friends. She could equally be feeling terrible but felt succumbed to peer pressure.
These are all possibilities but you really don't know what's gone on between the mum and her dd.