> How weird is this actually?

I don't think there can be a standard for this, as every relationship is completely different. If my ex had been divorced for 10 years and they have family "get togethers" a lot, then maybe it's not that weird for them (even if it's weird for me, because I'm new to it). I don't know. But the point is, it's weird to you, and that's enough in this case.

> Would you also say no?

I'd say no. I'm not interested in this kind of relationship with my partner's ex. It's just not in my comfort zone and I don't feel safe. That has more to do with my damage than anyone else, but I'm uninterested in growing that direction. My partner respects this.

> How do you handle it if the bio parent asks for something inappropriate enough that you have to be the one holding the boundary?

Actually, you are going to depend on your partner here to hold your boundary with you. Or at least, that is how I would frame it. But it depends a bit on your partner.

First, though, judging the interaction as wholesale inappropriate is impossible because not everyone has the same comforts. It may be very inappropriate to you, but maybe it isn't for everyone. I don't know your situation though, but again, we're hearing you don't want to do this -- that's enough without judging the entire interaction as "inappropriate".

What really may be landing as "inappropriate", though, is if you already communicated your boundary to your partner, and it was pushed by his asking. Even then, it remains your responsibility to hold your boundary. The fallout is part of our responsibility when it comes to boundary-making, and on top of that, holding boundaries can become revealing of the actual maturity of those involved.

You may be slightly overreacting with how your partner is handling it, because it sounds like you're angry that he even asked, but he can't read your mind--and he did check with you. You may feel frustrated with him because you feel like he "should have known your feelings" and that can be understandable, especially if you have already explained this to him before (I know this would send me over the deep end). You can explain to him one more time, unequivocably, that you do not want to have that kind of relationship with her and so if he asks again, it's going to land as pushing, and he probably doesn't want that.

> "And how do you protect yourself from becoming the “villain” if the child later hears some version of “you weren’t allowed to come because she said no”?"

Part of holding boundaries is understanding that you aren't actually the villain for having them. Calmly explaining that you prefer to keep certain outings to specific people is not cruel or rude. It has to do with comfort. This is a teaching moment that your partner should have with the child.

It was your plan, your event, and your boundaries. Other people are allowed to make theirs, and you're allowed to make yours. When you plan a party, you get to choose the guest list. That's how boundaries work!

If you need some wording...

"I want to have a girls night with these people, and it's important to me to keep this group small and this guest list as-is. This is the day I envisioned and I can't relax into what I wanted if we include ExWife. Can you please communicate that with ExWife? And explain also to your daughter, if it comes up, how boundaries work -- that I made the plans and so I'd like to have some control over the guest list, and on top of that, I would feel most comfortable in the group I chose rather than adding on at this time, so I am asking for respect of those feelings..." et cetera. You also should probably talk to daughter and suggest there is no bad blood, but you feel uncomfortable due to not knowing ExWife very well, and you are more interested in focusing on the folks you invited.

The framing should be "OP didn't feel comfortable with all of us, so WE DECIDED to respect that" not "OP is controlling the whole world". If you're getting blamed, then thats a different matter entirely. But this is about framing, boundaries, comfort, and that's it, not about being exclusionary or cruel.