(spoilers extended) Every time Jaehaera was called Aegon's heir:

"Queen Jaehaera's claim was as strong as the king's, and stronger in the minds of some, but the notion of placing that sweet, simple, frightened child on the Iron Throne was madness, all agreed."

"However, the war was far from won. Aegon was still at large, as was his daughter and remaining heir, Jaehaera. So, too, was Larys Strong the Clubfoot. The greater part of the chivalry of the west was dead or scattered, and the Red Kraken and his reavers still harried the western shore. More significantly, Prince Aemond’s campaign of terror continued in the riverlands."

"Barely a year later, in 123 AC, the fourteen-year-old princess gave birth to twins, a boy she named Jaehaerys and a girl called Jaehaera. Prince Aegon had heirs of his own now, the greens at court proclaimed happily. A dragon’s egg was placed in the cradle of each child, and two hatchlings soon came forth. Yet all was not well with these new twins. Jaehaera was tiny and slow

"You could perhaps make Ser Rickard’s ward be Jaehaera instead of Maelor, but Jaehaera can’t be killed, she has a huge role to play as Aegon’s next heir." (GRRM post)