"I think revenge is to move on and forget, not dwell." Is it your life? Your divorce? No.
Have you even been divorced?
"Why would you want reminding every time you sign something or get a letter (just examples)." This comment in particular suggests you haven't.
"she was born with a different name, that’s hers." Actually that was likely her (your?) fathers name.
Although to be honest I'm sceptical you're actually this woman's sister, I suspect you may be wife 2.
I still have ex's name as my name, I didn't want to change it in the immediate aftermath of the divorce as dd was very young and I wanted us to have the same name as each other. It's taboo to say but there IS still stigma over being an "unmarried mum" it's just less overt now.
It's also as pps have said an expensive (at a time when most women are really stuck financially anyway) pita to change!
In my case I also wouldn't want to go back to my fathers name as its a horrible name attached to someone & a time that I was really unhappy.
It's also the name that's on my professional & other qualifications and that most of my former employers & educational establishments know me by.
I was married only 10 years but had the name over 20 now.
As it happens my ex has remarried - and taken his 2nd wife's name cos he hated his (to him boring, he just aesthetically prefers her name and their kids have that name too)
You claim it doesn't bother you but it bothers you enough to have started a thread about it, whatever your genuine connection to the woman concerned, it's none of your business what name she chooses to go by.