OP - I completely get how you're feeling but are you sure there isn't a practical reason for this - e.g. the other mother might have asked for her DD to have a sleepover as a favour as she's out tonight? Or maybe she didn't want to drive so the sleepover mum offered and said the DD might as well stay over?
My DC are a bit older now but all kids come across this kind of thing at some point. I've found it's generally thoughtlessness on the part of the other mum, rather than malicious.
For instance, my daughter has a trundle bed which can be pulled out from under her bed if she has just one friend over, but if it's any more than that they tend to camp in the living room and it's much more excitement / less sleep all round. I would never knowingly exclude any child, but some mums just don't think and go with the simpler option.
If her daughter is fairly new, that mum is probably anxious about her settling in. She won't be fully aware of the history between your DD and the other girl. In any case, friendships at that age are in continual flux quite often. Maybe her daughter feels we is particularly clicking with the other girl this week for some random reason - e.g. They both like unicorns or the same sandwiches or whatever? She has asked her mum if x can sleepover and her mum has said ok without giving it too much thought?
It is of course possible that this mum feels she particularly connects with or is impressed by the other mum. In this case, There is not much you can do I'm afraid.
Maybe she can only cope with 2 girls at a time overnight and was planning to ask your DD next time? Simple as that.
Whatever it is, I'm sure she has no idea as to the impact of this sleepover on you and your DD.
As a PP said, 3 will be a tricky number tomorrow for rides.
I would suck it up for now, Go tomorrow, sense the vibe and make a decision from there as to whether to take a step back going forward.