If you have an abusive mother being surrounded by cards saying 'Best Mum in the WORLD!' and exhortations to cherish your mum because she has always cherished you, must be awful.
This.
MIL wasn't physically abusive (well, once, when she threatened the then teenage DH with a knife) but she was neglectful. DH had to look after his sisters while she docked about doing fuck knows what, he did all the cooking, got them ready for school and was on beck amd call whenever anyone wanted a cuppa but couldn't be arsed to walk twenty feet to the kettle. He didn't have a bedroom because they were in a two bed and she didn't want to move house, she was offered a three bed in the same street and refused it, so he had to sleep on the sofa meaning he had no privacy and couldn't go to bed until everyone else did. His sisters were dressed in brand new clothes, he was dressed in second hand stuff three sizes too big, including hand me downs from his overweight stepdad. When she had an affair and broke up the marriage, she blamed it on DH. She got him into debt once he was 18 as she talked him into signing this, that, and the other "for the good of the family", money he gave her for repayments wasn't passed on to the relevant companies. Even as an adult he was an after thought, one Christmas his (adult) sisters got brand new mobiles, £100 of shopping vouchers each, necklaces and more. DH got a tin of Asda biscuits. It took him many years to be able to stand up to her. In our early days she was okay, then we started planning to get married she literally turned overnight. That's when he began standing up her. I could list all the things gs she's said and done to us over the years but I try not to think about it if I can help it. She got worse when the DC came along and DH eventually went NC when she started leaving them out in favour of SILs DC (same age as ours). That lasted a year and she swore she'd changed, DH still wanted nothing to do with her but I let her see the DC. Nothing had changed and I eventually cut contact again. The final straw was when DS got £5 in a card for his birthday, dropped off after bedtime by MILs DP then on DDs birthday a few weeks later they showed up with a fucking tablet for her. We haven't seen her in nearly two years, despite her living around the corner, and while she stalks us a little bit sometimes (parking at the end of our street, doing "coincidental" drive bys at school run time, etc) it's been blissful.
Mothers Day however is hard for DH because, in his own words, he doesn't have a mother. Mothers love you and care about you, he just has That Woman who happened to give birth to him. And people feel the need to offer him their opinion, saying he should forgive her because it's Mothers Day. Get in touch and say sorry (!) because it's Mothers Day. It would make her day if he popped round with the DC because it's Mothers Day.
It's one more day and while it's nice to show your mum that you appreciate her, it doesn't cancel put the rest of the days in the year.