Hi rinobel,
My girl is Sec 1 this year. She also face the same problem last year when all her classmates and friends are taller than her.
However, by end of P6, her height suddenly shoot up and even taller than some of her friends.
This year sec 1, she even grow taller and she is now 163cm. So not to worry so much as long as she is healthy, exercise more, eat regularly, she will eventually grow tall.
Btw, my girl is attend Teakwondo weekly for the past 2 years, maybe this helps her.