Buggie:

I'm with you on this. To me, it seems like nothing more than a logistical issue: she doesn't have enough space to accommodate the friends she wishes to invite and their SOs. I'm guessing if she did have the space she would happily invite them. Why should she forgo inviting the people she wants to come to her party in favor of SOs she doesn't know? Also, she noted that she does not see these people very often, so, most likely, it's going to be an evening of rehashing old times, events, stories, etc. that the SOs were presumably not a party to and not familiar with. Wouldn't the SOs feel left out anyway? And again, it seems like a one-off event. I would imagine any reasonable SO would not take offense to this.

And, she's the one throwing the party and wants it to be a sit-down dinner, shouldn't she be allowed to throw any kind of party she wants? I think it's a pretty straightforward a reasonable request.