MissFenella, do you think all women are entirely defined by their relationship(s) to their husbands / partners, or is it just ex-wives? Pretty offensive, either way.
Your posts seem almost wilfully obtuse. The ex-wife has bowed out of her marriage, but there is no reason for her to bow out of her relationship with her children's grandparents.
The husband's relatives don't all belong to him, they're not part of his baggage. They are independent people with the right to form their own relationships: & in this case the husband's parents seem to have their own, independent relationship - which they clearly value - with their son's ex-wife / grandchildren's mum.
This isn't a case of whether the ex wife's feelings trump those of the current wife. It's a question of whether the current wife's feelings should be allowed to override the feelings, choices & values of her husband's family.
The idea that the the ex wife in this case "should feel awkward" is pathetic. Why should she feel awkward? Is she no longer of any value just because she's not this man's wife anymore? You have no idea of the depth of relationship she might have with her former in-laws.
And the idea that she has an "I was here first" attitude is pure conjecture on your part & sounds incredibly childish.
I acknowledge that OP's MIL may well not be all that nice, & may not be welcoming to her. If she'd posted about how her MIL was undermining her by comparing her unfavourably to her husband's ex, I'd have been the first to say she wasn't being unreasonable.
But the thread was about being irked by the PRESENCE of the ex. At events she has been invited to by people who have their own relationships with her & who value those relationships.
Nobody has the right to demand that people should write other people out of their lives / shared history / family just because they find their presence irksome.