Back to the original poster. DS completed GT Algebra I in 5th grade so similar enough to your situation. You already got really sound advice but ultimately you have to go with what feels right for your DD as well as yourself. I am with the flow of opinion to go with what works now so another vote for Algebra I in 6th grade.
However, I have to admit that I did choose against GT Algebra I in 4th grade even though DS was ready based on multiple assessments partly due to future considerations. My concern was that he may not be optimally ready to cover geometry and trigonometry in the depths that I wanted. It is likely that he would have been fine if we had chosen to accelerate another year but we don't regret holding back a year. His Pre-algebra curriculum was invaluable because it covered many geometry topics as well as basic trigonometry and it really solidified his foundation. Furthermore, his writing and computer skills are more advance now and more equal to the task of geometric proofs and mathematical software.
Thanks for sharing your child's experience. I also worry a bit about some gaps she may have in geometry but was reassured by the middle school that is should not be a problem... I hope so!
