How many would you invite?

[ColdAsConcrete]

DD (yr6) wants to do an activity for her birthday. Absolute max group size of 12, minimum of 6. Two places go to her and DC1. Cost is an issue unless she decides she wants to ask family for it instead of gifts.

There are 10 girls in the class, so 9 not including her. I'm thinking it's ok to invite 5 and so not invite 4.
But is it ok to invite 6 and leave out 3?
What about inviting 7 (and leave out 2)?

Less than half or everyone is the rule I go by.

In this instance I would invite four so you reach the minimum number of six.

Or invite everyone and the you're at 11 which is still lower than the maximum.

I would ask her to invite her closest friends, whatever that number is. DD (also Y6) is doing an activity for her birthday. We're inviting the ones in her class she's closest to, which I think works out to be about 8 of them (mix of boys and girls), out of a class of maybe 13?

Who is she closest to? Are there any lads she'd want to come? If there's no family going you could invite all 9 plus her and her DSis but are you saying you need spaces for cousins etc too?

She would happily invite all bar one (which I won't let her do).
She says she can't decide on only 4!
She won't invite any boys, never plays with them, her class is very divided (boys are very aggressive, they're having constant class workshops and outside involvement etc).
I don't know if not inviting two is too mean!

Is twelve to expensive op? If that's the case what CAN you afford?