I think there are quite a few that aren't nice/good MC out there. I didn't really like them that much though because, well, they actually had it coming. They deserved the bad ending.
I've read a lot of reincarnation stories but at this point all of them feel very cookie cutter with the MC always being "good", the only story I can remember having a MC that's still bad in her own way is "The villainess reverses the hourglass" which I think is a pretty sound manhwa.
If you remember any of those stories you've read about not so nice/good MC I'd love the recs because I'm sure I haven't read them yet ╮(￣▽￣)╭
The world isn't black and white and there's not rule that says only saintlike little goody two-shoes girls are the only ones that can have the time travel treatment. I think is grant she's like "I dug this hole I fell in but I'm still getting revenge on everbody else for that", like you go girl, go get your revenge and while you're at it maybe try and be a better person this second time around but is not a requirement.