To a point, you’re right, although its quite hard to really address because there aren’t many female murderers and the ones that do exist are almost exclusively white anyway. But there are cases which are uneasy / unsafe convictions but haven’t attracted anything like the furore this one has.
I don’t think it’s so much to do with her race as it is the crimes she’s been accused of. Female murderers are rare and the most notorious ones acted in conjunction with a ma anyway. It was always going to generate an enormous amount of publicity and press coverage and as such doubts creep in.
You might be interested to know the general feeling at Rose West’s trial was that she wouldn’t be convicted. Strange to think of now but that was the view of her barrister, as it was circumstantial evidence.
The only real equivalent case is Allitt and she was very different to Letby in all sorts of ways. There have been two other male nurses convicted of murder but both of those have had a certain amount of controversy; that said, it doesn’t look like they are getting out any time soon.