I can't get worked up over this.
The woman had a termination, as MIL accepts was her perfect right. She and her son were saddened by it - that's also their perfect right. Doesn't sound as though they berated the woman for it, but they are allowed to grieve privately while respecting that the decision wasn't theirs to make.
The woman terminated, presumably, because the relationship was all but over anyway. With that being the case, I don't know why the son should be obliged to be there.
As MIL acknowledges, the woman's own mother wasn't there, and the woman herself has a lot of sorrow in her life as well.
It all just sounds very sad to me. I hope they can all find peace.