How do her proportions look? My 2.5 yr old is all legs and all neck. He has no chest and is tall and lanky. You can tell he has plenty of room to grow. He’s about 15.2 hands right now and I’m certain he will make 16+ hands. Both his parents were ponies so we got some surprise height! But looking at his dam, you can see his legs are about 4-5" taller at the knee. There’s no doubt he will be a big horse.
If you want to know how much more a horse is going to grow, look at their legs first! And then look at pictures of the sire/dam and see how much muscle and development they have left.
Next October is plenty of time for your filly to reach the inspection height. I think you’ll be just fine.