I thought I'd post this story to illustrate what a big change can occur in a short time, with proper worming and feeding.
I bought an 18 mth old filly in February this year. She was underweight and about 13 hands high. I was expecting her to remain pony sized. Here is a pic the day I got her:
After being wormed (twice) she improved dramatically in weight, here she is about a month later:
The little white mini in the foreground is 9hh, so she has filled out but not up. Still 13ish hands.
Today, I measured her with a proper measuring stick, and she is now 14.2! That's in 6 mths. I was quite surprised. Here's a pic from today (it's winter here, so she's wooly):
I wouldn't be surprised if she grows even more before she's ready to break in :) She could end up 15hh!