Shen Shen had opportunity to practice her skills. She just didn't have a lot. The fact that Leetah said it was not often implies that it happened a few times at least. She also had to have learned it somewhere to be able to do it. Presumably, the SunFolk have continued to have children, if infrequently. I don't think it was ever suggested that the SunFolk had stopped breeding, like the Gliders. (Skywise definitely thought the Glider situation was weird- and if I don't think he would have reacted so strongly if the SunFolk were experiencing the same thing.) They just lived long lives and recognized not too often. But they seemed to have a healthy community. Their problem wasn't peaceful stagnation... it was that they had come to rely on others (Rayek, Leetah, the Wolfriders) to protect them, and they were too soft as a consequence. They needed to get tough. But they were still having kids and thriving as a community in their peaceful oasis the whole time. The statement "there are no other young cubs here" is different than saying "there are no other cubs here." There must have been some young adults at that point. Shen Shen probably doesn't have magic. But she clearly has an instinct for and interest in healing. (It seems to run in the family, right? Toorah was the one who stitched up Rayek.) At the very least, Shen Shen cared enough to learn from Old Maggoty. I don't think she is going to outshine her sister- and certainly not in terms of healing magic. She is different from her sister. I think her lesson is going to be to learn to feel she is special in her own right, without having to compare herself to or compete with Leetah. Her dream wasn't about outdoing Leetah- the message was to "shine where you love." She's going to discover what she loves and find her path.