Anti heroes? It's almost impossible to find little old ladies (or even middle-aged women) as any kind of main character in fantasy and SF.
There's Granny Weatherwax and Nanny Ogg in Pratchett's stuff.
Hmm, the only other one I can think of off the top of my head is Sherri Tepper's
Beauty. The character started out young, but she aged as the story progressed. I think there were some trips to the land of Fae involved, however. It's been a while since I read it.
Paladin of Souls by Lois McMaster Bujold has a middle-aged female protagonist, but yeah, even middle aged, let alone much older women, are really under represented as focal character in fantasy and SF.
There's a great older woman character in Glenda Larke's Stormlords books, but she's not a pov character, more of a mysterious figure who is leading a rebellion. But cool to see.
In the movie
Willow, the wise old wizard mentor was a woman, which made a nice change.
None of these are really anti heroes, though.
Here's a link to an article on Tor's website about this very issue. The lack of interesting stories and movies with female protagonists past very early middle age is not confined to SFF, of course, but I think the issue is particularly bad in this genre. Very old men aren't crawling out of the woodwork in fantasy either, except as wise old mentors, but there are a number who are middle aged, at least. And they rarely seem to have trouble finding younger women who want to sleep with them either.