I was thinking that just this morning when I brought up Jon Snow and how a lot seemed to be coming together for him but that I had a bad feeling about it; and that is that I feel like GRRM wants a female to prevail. It’s not based on anything I know about him, or his books, just a feeling I get, or a kind of gestalt undercurrent from the whole body of work to date.
The obvious female would be Daenerys, but for that very reason, might not be “bittersweet”.
On the other hand, more than just bittersweet, for a lot of people, Cercei getting the iron throne after all would be more like a bitter pill.
You have a couple of outside shots at it, but two up and coming females are the siblings Arya and Sansa. That would be bittersweet because it would entail Jon falling out of it.
There are other long shots even more difficult to predict; What claim could Gilly ever have? Or Missandei? Same with Brienne who I think is of nobility but not lineage to a house.
Also, did the red witch die?
Brienne is the sole surviving child and heir to Lord Selwyn Tarth. Lord Selwyn is the Lord of Evenfall Hall, which is the seat of House Tarth. The island of Tarth is located in the Stormlands. So, Brienne is of noble birth, but House Tarth is one of the minor houses of Westeros. Her claim would not be very good.
Gilly would have no claim. She is one of Craster’s daughters and a wildling.
Missandei is a foreigner and a former slave. She would have no claim.
Arya has the skills of the Faceless Men. She could pretend to be anyone (once they are dead and she takes their face). I could see her killing someone (Jaime Lannister?) so that she can get closer to Cercei.
Melisandre (the Red Woman / Red priestess) is still alive. She was exiled from the North by Jon Snow. She was last seen at Dragonstone. She was heading for Volantis, but said that she must return to Westeros once more to meet her end.