Is it ok to plan a girls' night, but exclude my lesbian friend's partner (read details)?

Say we are having a "girls night out" no spouses. That way we can all feel free to ask questions or gripe about our spouses. Tell her no spouses (gay or straight allowed) She will probably appreciated being seen as any "normal" couple.

What you can do is make it an invitation-only event, and just don't invite her partner. Her partner shouldn't feel excluded unless she would otherwise have been part of the group, but from the sound of it she's only tangentially included in the group. You're not really excluding her, you're just failing to include her; there's a difference. If, when you invite your friend, she asks if she can take her girlfriend, tell her it's invitation-only but she's welcome to talk about her girlfriend to the group, that way you're making it clear that you don't disapprove of the relationship.

My girlfriend and I have the understanding that girls night is really "people you're not sleeping with night". The whole purpose of a girls night is to get together as just the girls, and honestly it gives you the opportunity to talk about things going on with you and your spouse that you normally wouldn't say in front of them. (I'm not saying talk ABOUT them, just to clarify). Tell your friend is a couple free night and she should understand.

Girls night out is not about having girls only.. it's about being with your friends only, to let loose and not worry about partners expecting certain behavior

that would com across as dis approving

if you want to catch up with you friend ask her to go out with you for coffee and talk to her then