Regarding divorced women, I don’t know what the halacha is, but divorced mothers generally feel that they want to continue covering their hair regardless because it’s bad chinuch for the kids. Also, it could be maris ayin if people know they have kids and don’t realize they are divorced. Plus, it would be very awkward and uncomfortable for the kids.
I knew one widow who only became Frum around the time she lost her husband. At the beginning, she was more modern and didn’t cover her hair, but at some point, she became more Frum and started covering her hair.
A few years later, she was told by a Rav (I do not know how reliable he was or wasn’t) that she doesn’t have to cover her hair.
I told her that even if that were technically true, it would be very bad chinuch for the kids especialy since she only started covering her hair after she became widowed. So to start and then stop is very bad chinuch. She agreed with me and continued to cover her hair.