It might look that way but not everything scales with height, even short girls have certain proportions to their hips since it needs to be that way for childbirth to be viable; men twice a girls size will still have more narrow hips. Thats why some short girls seemingly have huge hips compared to taller girls when in fact they are just the same size and it looks that way because the rest of them is smaller.
This actually happens with many body parts, your eyes are a good example, they grow far less in size compared to other body parts from when you are a child despite you more than doubling in size overall since they need to have certain proportions to function correctly.
Short girls looking like they have thick thighs and wide hips is normal. Also, Kitty is an X-girl, she has a MUCH more intense workout regimen compared to an average school girl, her being built like a volleyball player is not unusual.
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