I was married to my late husband for 27 yrs. His ex chose to keep her married name, presumably to have the same name as her adult children and also because changing would have been a faff.
It did cause me a bit of inconvenience at work. She met her Affair Partner at work, in a school.
I worked in a school in the same region. The way that emails were set up would have meant us having almost identical email addresses and I could see that there would be confusion in other ways. Partly because of that, I kept my own name at work for the first 8 years. I just sucked up any confusion outside work.
Things did take a weird turn. When her AP died, she finished up with DH's best friend, a widow. When he died, I helped her out with a hospital appointment - she needed a day procedure, the kids weren't stepping up and DH couldn't drive by then.
I dropped her off. After I got the phone call to pick her up, I discovered that she'd put me down as her Next of Kin at hospital. That made me feel a bit uncomfortable.
I'll cut this short, but suffice to say that by the time DH died, his ex had Partner No 4 who dropped her off at DH's funeral and some strange things happened around that time.
Ergo, when I had to sort out the enscription on the memorial I followed the old Scottish tradition of putting my maiden name instead of my married name - I wasn't risking people thinking that it was her. (At a point when I was on my own, trying to keep the last of my sanity whilst organising a funeral during lockdown, I'd got a phone call from DH's DIL, telling me that the ex was "devastated"...)
So...I can understand your feelings, @ByCyanPlayer - but I voted YABU. For the reasons that I outlined at the beginning, it's often sensible for a divorcee to keep her ex's surname.