My DD had great friends when she was essentially with kids her own age, but in school she kept very quiet because it was so important to her to fit in that she didn't want to stand out by showing she already knew everything they were learning.
When she grade accelerated she again easily made friends with kids in her class, but now she began to speak in class and could answer questions in class without worrying so much about what the other kids would think since she was more on their level.
When she switched to a school with a lot of redshirted girls who were even older than she was, she made the best friends she's ever had and will readily answer questions in class because she feels like she truly fits in.
I really feel like she would fit in and make friends with girls of any age. But, I think now she's found her true peers with girls 1.5 to 2+ years older than her.
I should add, though, that my DD is slightly tall for her age and has never been the shortest person in her class regardless of grade, so I'm not sure if height would have played a bigger role in our decision making if she were very small.
To me, I think it's telling that your DD picks older kids when she has the say as to who she socializes with.
Will any of your DD's classmates at her private school be going to the other school when your DD changes schools? You may find that she balks at not moving up at the same time as her friends do. I know my DD would have!
