Princess Rhaenyra was killed by her half-younger brother, King Aegon II. In front of her own son, Aegon, who was keep as a prisoner. But was saved by Lord Cregan Stark himself, and take him to Dragonstone where his half-eldest sister, Princess Jacaera lives with their family who takes their side. The Princess has lost her two brothers, Lucerys and Joffrey, her half-youngest sister, Visenya, her fathers, Ser Harwin, Ser Laenor Velaryon, and Daemon Targaryen, and her very own mother, The Heir to the Iron Throne, Queen Rhaenyra Targaryen but she was never Queen but stayed as Princess. When the greens stole her Throne and put her usurper brother, Aegon, who was now King.
(And also this is not an Oc, this is Jacerys as a girl.)