Well just because its a habit since college, life changes after marriage. and there must be underlying reasons for her to act the way she does. yes we did grow up in gender mixed environments, it doesnt not mean you can hide away from your own culture and values. maybe she still has her eastern values where segragation especially between friends is a must.
in my own family we all sit together, my best friend is my very own brother in law, but because we are family, we sit together.hubbys friends and their wives is another story.
i have a funny feeling this woman, may be either jealous of their wives, are they smarter/prettier/ whatever than her…
or
she just doesnt feel as included, inviting her is one thing, actually including her is another.