My mum is around 5'6" and my dad 5'9" so I'd be expected to only be around 5'5" but I'm roughly 5'7½". Defo didn't stop growing 2-3yrs after starting my period (I know that's just an average), but probably closer to 5 years after, though growth from that point was definitely slower. It probably varies based on how young you were though with younger starters continuing to grow longer but don't quote me on that
Height isn't entirely biological either (thought to be about 80% bio).
Its also about nutrients (especially calcium and protein) as well as sleep and an appropriate amount of exercise.
We've mentioned before that their diets haven't always seemed varied and they rely on supplements or did anyway so there is a possibility she lacked some nutrients in the vital time frame.
Shes mentioned before that people are shocked at how small she is because she looks average height on camera. You can sometimes see when she is with friends, especially guys, but not usually.
You didn't come across as being critical to me, just observational. They, on the other hand, like to make fun of the size of Sienna's feet all the time and then post about people all being different and learning to love your body