C.H.
You don't really want your daughter being by far the youngest kid in the class. Just teach her all the cool stuff at home (reading, science kits, etc.) and send her next year. Some of the kids will be up to two years older than her if she goes to kindergarten now, because so many people hold their kids back (Some do it so that they are bigger when it's time to play grade-level sports and the others do it because their friends did it.) Those older kids might be 6 3/4 while she's 4 3/4!
I was very tense about this with my first daughter for several years, actually, but now that she's in seventh grade, it's been obvious for a few years that she's exactly where she needs to be.
I will say that these schooling decisions and sports decisions and such become a lot easier with the second and third child.