I think it has a lot to do with your specific child and his/her personality, learning style, etc.
Our son would have qualified for kindergarten in 2005/2006 by two days (cut off was September 30. His birthday is September 28.) Like your daughter he would have started kindergarten at age 4 with kids who were as much as a whole year older than he was.
I spoke at length to his preschool teachers, friends who are teachers, etc. One thing that one of them told me was: They've met several parents who wished they'd started their children late in kindergarten, but didn't. But they'd never met anyone who'd started their kid late in kinder and regretted it. (Some might not feel it made a difference, but no one regretted it.)
We chose to start our son this year (2006/2007) instead. Tomorrow is his last day of kindergarten. I do not regret our decision. He, of course, knew his letters, numbers, shapes, etc. from preschool -- but you'd be surprised what they expect kindergarteners to know these days. DS is reading on his own. They've learned about tectonic plates in the earth's crust and 3D shapes like spheres. I *know* we didn't cover that stuff until much later in school (probably not even in first grade.)
In addition to that, DS is generally a very good kid but he had a tendency to "go with the crowd" even if he knew they were making poor choices. The extra year has given him the confidence to make choices for himself, even if it means going against what his friends are doing. I think the extra year of maturity helped with that.
Thirdly, our school does full-day kindergarten with no nap/rest period. Last year, at 4/5, DS still *needed* that nap and took it without complaint. (He's always needed a lot of sleep.) I think the full day with no nap would have set him up for failure.
My DS is doing well in school, but he's not bored. But, this first year has given him a very positive outlook on school in general. He loves it and is eager to learn. Part of that is because he had a great teacher. But I think part of it is that he was really ready to go. I hope we can continue to foster his good attitude toward school because I really do think that goes a *long* way toward success.
So -- anyway -- you're the best person to judge what's best for your child. Chances are you'll "make it work" whichever way you go. I think DS probably could have succeeded last year, but I'm not sorry we waited.
Good luck with your decision.
p.s. For what it's worth, I hate the term "red shirted." I think that implies we held our children back so that they'll be bigger, older and able to be *better* than other kids. That couldn't be farther from the truth for me -- I wanted him to do well on his own right (against the curriculum, against the schedule, against peer pressure), but it had nothing to do with being better than other kids.
Edited to add: I would not hold my child back *just* because he'd be the youngest in the class -- because no matter when they set the date, someone's going to be the youngest. (I was nearly the youngest when I was in school.) But I did not feel my DS was ready to go at 4 years old.