Well, it depends! And you need to give us a lot more information:
What do you do with your pony? Pleasure and trail riding? Showing? What kind of showing? Some disciplines put a lot of emphasis on suitability (rider to horse size), others do not, and it always matters more in classes where the rider is judged.
How old are you now, and what does your doctor predict your adult height will be?
If you're going to be 5' - 5'2", you continue to be slender, your pony is big barreled and you're not showing equitation, you might well keep riding her until you're an adult! But that's a lot of ifs!
Why don't you give more info and perhaps even post a photo, and posters can give better advice?