Op it’s not just you, some of these responses are beyond unhinged. Please try to step back from the vindictive nastiness you’re being urged to carry out.
as said, unless this is a whole class party then there is no issue here. Children can be friends with whatever child they wish, irrelevant of gender, your child isn’t entitled to attend another girls party over a closer boy friend, by virtue of her being a girl. It’s a terrible message to give her.
nor should you be deciding who attends her parties. That’s her call.
has she a dad who is involved? If you struggle to cope with this sort of thing, if there is, maybe you could ask him to help you?
mines a young adult now, and you’ve a long road ahead. Finding out what’s the situation here, talking to your child, the other parent if necessary, is the way to go, not some well I will treat them worse vendetta. It only harms your child and ignore anyone urging you to gp that route.