My son is not G&T, but he is doing very well in year 1, excels in maths and nature related topics. He is very well stimulated, he is tri-lingual, has violin lessons, karate and tennis, drama club and does physics and chemistry experiments with his dad daily. We also go on many outings, wetland centre, botanic gardens, etc.
I agree there is a lot you can do outside of school that will keep her challenged.
We are facing abit of an opposite problem now, as we are moving back to Norway where they start school at six. So, he has already had nearly two years of schooling. But the head teacher is unwilling to place him in a class above as they think it very important to stay with their year group, for reasons of social maturity.
I know my son, he is a mixture of on the one hand "old" for his age, yet he can be very "childish" and full of a six year olds sillyness if it suits him.
This is what our new school is proposing:
He will start in a small G&T fast track class of 6 year olds starting earlier than the school year, but incorporated into the current year 1, now in April. These children will receive teaching tailored to their skills, but in the year 1 setting.
In the automn, the headmistress will decide whether he shall move into the new year 1 or proceed to year 2 with the current year 1 group. He will receive English tuition with year 3 or 4.
I think you should talk to your headmistress as soon as possible, as I am sure they would be keen to accommodate. It might be better to stay in her year group, but maybe join other classes in fields where she is ahead?
Good LUck.