Life and it's changes are is always interesting Greenlotus and you may well have seen similar things that are a bit sad if you hadn't accelerated. Kids, their interests and activities and friendships, change a lot year by year. It is possible that your DD may have grown apart from her old friends anyway as her interests become more divergent. Changing friends as kids change schools is also normal and in many ways quite healthy.
We didn't have your challenges on the sibling front but we have done a lot of school changes and two accelerations and I can sympathise with you and your DD but also offer hope. My DD has never been happier or more focussed since her last grade skip. She has moved apart from a girl who everyone said was joined at the hip with my DD and that is ok. She is till friends with other kids from her previous year and years below that but she is with a group that are on the same wave length as her and she is relieved.
All change is hard and there will be bad with the good but that is life not just acceleration. While other parents responses are also interesting, it is more about ignorance than anything else. Respond with how interesting and move on!
Congratulations to you and both of your children as this has been a difficult journey and you are all doing well.
