When is a kitten fully grown?

This is probably a stupid question considering the fact that I have two other cats. But I have a 9 month old female pastel calico who is still really tiny. Shouldnt she be almost done growing? We got her at 2 months and she was super tiny, smaller then most kittens but she was not a runt, her parents where small also. Could she be done growing at 9 months? I really would like her to stay this small becuase she is really cute and so much smaller then my other two. The vet seems to tell us she is healthy so I'm sure it's not like a health thing. Shes not under weight or anything just small. She looks like about 6 months and is going to be a year in march.