Try to find the good in this person. Surely there must be something about her - after all, your Dear Son married her and has stayed with her and together they have raised a family.
Think about this.. does she work? Maybe she cooks? Does she seem to love the girls and your son? Perhaps she is a kind person, a loyal one? Maybe she’s witty, creative or has some other skill. Once you start to notice these things, I think you will warm to her, and then you’ll be off on a new, and hopefully, happier trajectory.
Good luck.