TheNorthWitch:
I agree the OP does not have to be concerned about this woman's social life, or lack thereof. She doesn't want to be friends, which is absolutely her right- but surely she can decline invites/friendly overtures without being rude or unkind?
This woman has not "ruined the OPs social plans"- she accepted an invite from a friend (the OPs husband). Which is an entirely reasonable thing to do. I doubt she thought that she would not be welcome- given that the invite was from a friend.
I wouldn't have thought the OPs DH said "well, my wife won't like it and neither will our friends, but why don't you come along to upset them all and ruin their night" so it's not like she would know she was stepping on OPs toes.
Conversely, this woman has no responsibility to OPs social life either- she was accepting an invite from her friend and not OP. She can only assume the person who invited her is at liberty to do so. And as much as OP doesn't have to give a fig about this woman or her feeling- surely this works both ways? This woman does not have any responsibility towards OP (especially as she probably didn't know OP held her in such contempt).
It's the OPs DH who was responsible for considering his DWs and other friends wishes regarding inviting others. It is not up anyone he invites to try and second guess what his wife/other guests may or may not feel about it all.
The OP, had she been acting like a considerate adult, would have been better bringing this up with her DH- and if she could not tolerate this woman being in her presence, asking her DH to explain it to his friend.
And if she thinks there is something untoward going on between them, she would be better off broaching this with him. As opposed to being rude and unkind to a friend of her DH, who may have done nothing wrong.
If there is nothing untoward between her DH and his friend, I think the OP would be very churlish and unreasonable to tell him who he could and could not be friends with. If there is something going on, she's be better off tackling it head on and deciding what to do about it.