Jinora was the first to realize the magnitude of her and her siblings' situation. After all, they were younger than her and cared more about having fun than contemplating serious life matters. But when Jinora was old enough to take out a flying bison by herself, she began to think about what it meant to be one of just a handful of airbenders in the entire world. Across vast oceans, throughout gigantic land masses, benders existed in multitudes, but they answered to the elements of water, earth, and fire. There were precisely four airbenders out of hundreds of thousands of people, and the only ones that could join their ranks were Pema's unborn child and the current Avatar, Korra.
If any nation had to depend on only a few people for survival, it was best it was the Air Nomads, Jinora mused. They could stand up to the pressure of having to survive for the sake of the world's balance. Daily meditation, studying ancient philosophies, and practicing airbending techniques all served to keep the Nomads peaceful and level-headed. For someone like Jinora, who was intelligent and thoughtful enough to understand the high value of airbenders, these things were necessary to relieve the pressure of being born at such a critical time in the history of airbenders.
If anything happened to her father or siblings, what Fire Lord Sozin had attempted so long ago would finally be accomplished. Tenzin was getting older and if Ikki and Meelo's current personalities were any indicator, neither of them would ever learn to take their situation seriously. That left it to Jinora to be careful, to take every precaution for her and her siblings' survival. She constantly volunteered to babysit Meelo and whenever Ikki's ideas got a little too outlandish, she would put a stop to them or get one of their parents to.
It would be one of their not-so-distant descendants that would one day be declared the Avatar's reincarnation. Depending on how long Korra and the next two Avatars lived- well, it was unlikely, but Jinora might even see her great-granddaughter or great-great-nephew given the sacred title. And Jinora couldn't think about that without also considering the unspoken duty she and her siblings were given. It was the same duty Pema happily accepted when she married Tenzin. They were all expected to marry and have plenty of children to help replenish the airbending population. Jinora was beginning to notice boys and think about how attractive she found different males, but knowing that marriage was basically a requirement for her made the prospect that much less romantic. This was one reason she sought refuge in historical romances, filled with lovers whose only motivation was passion for each other. They never had to think of the needs of the world before their personal desires and it was beautifully selfish.
Air Nomads, however, were not selfish. They could withstand any amount of pressure. They could handle upholding the world's harmony because such teachings were the pillars of their culture. Yes, it was a heavy burden on Jinora's shoulders, but she never doubted she could handle it.