MIL Anniversary upset - have we done wrong?

[CharChar91]

For context, approx 2 years ago my MIL cheated on her husband of 38 years with an old flame from Malta on a 2 week lone 'holiday'. The next January she announced she was going to move there with him. Broke FIL's heart, obviously. Large house was sold (their retirement fund) and she took well over half the money. She went, she's been flitting back and forth between her two lives since.
Family is ruptured, there are a lot of big feelings and arguements. FIL has done amazingly well but being in love with her and the laid back man he is he allows her to stay with him when she's 'home' (he even gives up his bed for her and sleeps in the spare, single bed). He bought a 'doer-upper' cash with his money and has gone back to work to top up his state pension to live and fund renovations.
Divorce proceedings were started, neither have signed the final paperwork yet but it's not openly discussed.
Shock, the grass wasn't greener. MIL has broken up with new man (following his prostate cancer and subsequent undiagnosed depression) and returned. She's staying with FIL.
They came round for lunch on Saturday, awkward but we just leave the subject as the elephant in the room to avoid conflict. We all had a nice time. It happened to be their wedding anniversary but for obvious reasons we didn't say anything, despite MIL making a point of the dste.
My partner went round yesterday to see MIL. She was upset that we didn't mention or celebrate??/mark the occasion. Partner laughed out loud in disbelief. She was cross and it's another way her children don't appreciate her/respect her etc etc.

He came home and spoke to me last night and we can't see that we were in the wrong? If we had mentioned it on the day would that now have been an awkward and disrespectful thing to say?
So fed up of the whole situation and subsequent drama for 2 years, it's so draining.
Have we been unreasonable for not acknowledging their anniversary?

Some people might find your MIL worthy of enormous respect for the sheer front of expecting everyone to ignore what she's done and and shaping her new narrative where whe's the heroine of her story while being unfaithful and taking most of the assets, arranging the 'holiday' while married and expecting everyone to pretend to believe they met by accident, dumping the BF when he developed cancer and trying to return to the FIL, all the time putting herself ahead of everyone else. Many psychopaths, sociopaths and narcissists would respect her absolutely during the annual get together.

Tell her you gave her marriage the amount of respect she has.

I am going to go against the grain here and say that your mil might be a hideous narcissist but there are two sides to every story in a long marriage , and while she sounds like a rl version of Bridget Jones's mother, she may have had legitimate reasons for being unhappy in her marriage, which prompted her recent poor behaviour. On the one hand it is great that your fil is laid back but living with an eternally passive man isn't always easy. I am not saying her actions were right but when pps refer to her "upsetting the family" what I personally think is that the family should butt out and it's between her and your fil how they should proceed (or not) in their relationship. Whatever you may think of her, she was married to your partner's father for 38 years, and surely that counts for something? I would not recommend a renewal of vows as every single couple I know who has done this has split up a year or so afterwards. If your dp had a problem with her protesting about not mentioning their anniversary, then he should have had the balls to say something then and there. Other than that, I would leave them alone to sort out their marriage in private.

I kind of agree @Mintchervilpurslane - but MiL has made your sensible approach impossible by demanding that her children congratulate her on her wedding anniversary, & then being performatively "upset" that they were too embarrassed to do so.

what I personally think is that the family should butt out and it's between her and your fil how they should proceed (or not) in their relationship

When you start airing your dirty laundry in public and kick off when they won’t celebrate a sham anniversary you lose the right to privacy.

Did her husband take her back? And in this case maybe they have decided that her affair did not exist and therefore their wedding anniversary is on.aa

Absolutely agree.

Next time say loudly 'it's a WEDDING anniversary, you can't celebrate that after you left for a year..!' And look at her like she's crazy (cos she is!)