About two years ago, following the breakdown of her marriage, my DSis had a fling with our stepsister's husband. It was a one-time thing, my DSis and SS's husband moved on and it was all kept under wraps, though I and my DF (married to SS's mum) knew about it.
I should add at this point that DF and SM have only been married a few years and we are not particularly close to SS, I personally have only met her a handful of times as we live in different towns.
A couple of weeks ago, SS's husband was caught out sending naughty texts to another woman (who was not interested and who told SS). In the interest of clearing the air and thinking it would help repair his marriage, SS's husband confessed all to SS.
Of course, massive shockwaves ensued, and SS and her husband have now split. SS sent a string of nasty texts to my DSis calling her lots of names etc.
Unfortunately, this happened about a week before my DF was due to celebrate a big birthday. He had a party booked and everything, but because of everything that was going on, he decided to cancel.
I have a disabled DS who finds social gatherings very stressful, and for whom I have problems finding a babysitter. So rather than go to the party, DH and I suggested that we do a nice dinner for DF and SM at ours. This was all planned and arranged before any of this happened, BTW.
Last night, DSis phoned to ask if she could tag along on our dinner. Offered to contribute, and help cook etc. This is all fine with me, but I did say to her that it wasn't just DF coming, and that SM was not keen on seeing DSis just yet out of loyalty to SS. I suggested that DSis phone up our DF and sound him out about it.
DSis was very angry with me, saying why should she be the one who was punished and not get to see DF on his birthday. She thinks I should uninvite SM out of loyalty to her.
I replied that I thought if she wanted to clear the air and put her feelings across, that speaking to DF and SM herself was the way to go. But DSis said that she didn't care what SM thought of her anyway.
So it seems to me as though she wants someone to stand up for her point of view and challenge what she thinks of as unfair treatment, but she doesn't want to do it herself.
From my perspective, I think that I had invited SM before any of this happened, it's not her fault, and that she is feeling loyalty towards her daughter, who after all must be reeling right now. She hasn't said she will never see DSis again, just not right now.
I also think that whatever the circumstances, DSis has done a really shitty thing to SS and should really take it on the chin a bit. I think she is a bit surprised at how angry and upset SS was, which I am baffled by.
DSis seems to think they should all just get over it as it happened two years ago and wasn't a big deal. And that I am being really disloyal by taking someone else's side.
So, AIBU? I think this really isn't a battle I want to fight on DSis's behalf.