You should start using timothy hay or at least mixing it in because she is old enough and timothy is better for them once they are old enough. Because the nutrients in alfalfa is in most of the pellets
As for the pellets you cant really go wrong of course the food with higher nutrition is better but as long as your bunny likes it is probably ok. usually any food at a pet store is fine for them. When you go to the pet store you can ask them for higher quality food and they should know some.
You wont upset her tummy unless she doesn't like it but my bunny likes everything!!!!