Rhaenys Targaryen (Nymeros-Martell) days before the Sack of King's Landing, where she was brutally murdered by ser Armory Lorch... At least that's what is known.
Swapped for another child, she grew up in the guise of Rhea Sand and under the tutelage of her uncle, Oberyn Martell, she became a Sand Snake. Marks on her body remind her daily of her goal of revenge, but not as a pawn of her kin, but as a player in Game of Thrones.
She pulled some traits from Oberyn. She has a widow's beak and over time her eyes took on the shape of the other Snakes.
She doesn't have dragon dreams, or even a dragon. She is "much more Dornish/Rhoynar".
Her story revolves around many conflicts about the uncertainty of who she is, what she is for and if she is really making the right decisions. She was born with the possibility of holding great power (a possibility because she is a woman, despite being a firstborn), something that for her is not a birthright. It's more like a weight that only SHE has the strength to hold... But does she really have it? (She has some contrasts to Maegor in many ways)
Either way, she's very much a player. Not on the level of Tywin or Varys, but she certainly knows how to put the pieces together and move the game in her favor. Besides, she's a witch.
The correct nomenclature for the magic system I created for my ASOIAF AUs would be: Witchcrafter. I didn't develop that beyond the fact that it involves her falling into a river on a trip with Oberyn in the Free Cities. Anyway, this magical side helps her to be a dangerous player.
In terms of skills as a future queen (?) She was educated from a young age for this future position. Doran believes her to be as smart as Alysanne. And in battle/open conflicts? Well... Remember those contrasts with Maegor?
Love interests? I don't really like the stereotype of the sexy Dornish, and neither does she, but as a player, she uses all the cards. Her first major relationship is with Robb Stark, but unlike many fanfictions in which the character who stole the title of love interest from the original becomes enemies, Rhaenys seduces Jeyne as well and brings her to her side as a political ally. As you may have noticed, she doesn't really fall in love with Robb, but the only one who notices this is Catelyn, who thinks this girl is not who she says she is.
Anyway, these are just ideas from a fanfic that only has a prologue in Portuguese and that can be found in my Google Docs. It may never see the light of day, but if it does, I'll let you know.