Some breeds of cat (maine coons for example) carry on growing up until the age of 4!!
A cat between 7-9 months is definitely not fully mature, and still could have a couple of growth spurts yet.
My russian Blue was still pretty small at that age, and now age 2, he's massive! I remember a stage he went through where his body seemed to be growing, but his head seemed to stay really small, but eventually it all evened itself out!
Its also hard to remember how tiny she probably was when you got her, find some pictures of her when she was 8 weeks old, that'll make you realise how much she's actually grown!
Calicos are quite naturally petite cats, and females tend to be on the smaller size anyway. I really wouldn't worry, no doubt she's got a lot of growing to do yet, so long as she's feeding and drinking well, she'll be fine.