My (potentially controversial, so apologies) theory goes like this:
Devin's self-insert/'Mary Sue' was Nightwing.
Evidence:
1)Devin Grayson was not born Devin Grayson, she changed her name to denote her deep identification with the character.
2)A lot of the meta and fanfic she's written re: Nightwing's sexuality overlap with much of what she's written about herself in those areas.
3)Reading the Nightwing/Tarantula debacle felt like listening in on somebody's therapy session.
This isn't to say that all of her stories were awful. I liked quite a few of them. I even used to regularly defend her Nightwing and Titans work on an old Titans mailing list I used to belong to. She did a lot interesting, character driven stories that stood out from what the rest of the Bat-writers of that era were doing, and (usually) in a good way.
But she sometimes objectified and fetishized the character to a weird degree, and some of those weirder story beats, IMHO, read as if she regularly vacillated between wanting to do Nightwing or be Nightwing -- sometimes within the same issue.