Hi, T. --
This is a subject people seem to be very opinionated about, for sure! My daughter is only 3, so I have a little time before making this decision for her, but I can tell you how it was made for me.
My parents sent me to kindergarten when I was 5, but I was alread able to read and got incredibly bored with what we were supposed to be doing in class. I knew both the kindergarteners and the first graders, having spent the summer with them at summer school, so my parents petitioned the principal to let me skip to first grade. He was extremely reluctant, and I remember having to be interviewed by him so he could get a sense of my developmental level.
Anyway, apparently he gave his guarded consent, and I skipped ahead to first grade, where I was still bored due to the lack of challenge in reading, but not quite as bored. By the time I got to third grade, my skills were no longer so advanced, and I settled in to being just as challenged as everybody else for the remainder of my education.
I was always the youngest kid in class, but it never made a single whit of difference. In fact, I don't think my friends ever even knew. It was not until I was in high school that I had a classmate who was younger than I was - having skipped 2 grades. She was as well-accepted as anyone else, and went on to be an optometrist after college.
Anyway, my experience of being put into school at 5 and then skipped ahead to the level of challenge that was appropriate for me was 1000% beneficial. I didn't have any trouble making friends, I loved school, and I continued to be a good learner. I graduated Cum Laude from several honors programs in college, with a 3.9 GPA. In high school, I'd been class president, prom queen, and editor of the school paper... I mention these various things just to say that I didn't suffer any negative consequences from being skipped, and, in fact, I think it was the best decision my parents could have made -- to keep me challenged and happy.
One decision certainly does NOT fit all, but I think you should not fear putting your daughter in school if she is socially and academically at the stage of her peers. Her age is pretty much irrellevant, at least in my opinion. Age is one of those things that becomes more and more arbitrary the older you get. My daughter is already reading, but her friend who is only 4 months younger, is still only barely speaking. For her, going to school early is more feasible. For him, I don't think so. It's all got to be according to your feeling about your daughter's level. I think you could also benefit from talking to some teachers at her potential school, and the principal, too, to get a read. You can also ask the opinion of her current teachers. I would say, though, it sounds like she's doing just great, so go for it!! Above all, whatever your choice, have confidence in her and challenge her. I'm sure she will rise to your expectations, as long as they are made with love and with her best interests in mind.
Good luck!
H.