You are all wonderful! Thank you so much all those of you who commented!
It was really helpful to know that I probably wasn’t totally over-reacting or being over-protective and I did as you suggested, talked to the mother and she is happy to be present, if hidden in an upstairs room, during the party. We did have a bit of a grim evening (before I was able to talk to the other mum), but things seem to be back on an even keel this morning.
It’s lovely to know that I can draw on such wisdom!
PS More later….I’m getting the sewing machine out. I think I’ve earned a little me time!