First find out what subjects they believe she's g&t for.
Then ask what levels she's at (to gauge how far above average she is). Its a bit more difficult if shes g&t for art & music, but if its numerousy, literacy, science then they should be able to give you her NC levels. If she's yr1 average child will be expected to get 1b by the send of this year, end of year 2 expected level is 2b & for some perspective, end of year 4 is 3b.
Next ask about differentiation. The school will have a g&t policy document, (which may have come with the letter you received, if not ask if you can have a copy). Examples of things they might do are move her up to the next year group for maths, (if that's her strong subject), or there might be a couple of dcs working at a similar level in her strong subject(s) so they might do in class differentiation, (they do this in my dcs school).
Also, ask if there are any other advantages to being on the g&t list in your area eg interschool masterclasses, special day trips, a science club or whatever, so you can make the most of the opportunities.