My parents "held me back" an extra year when I was a young child before sending me to school. My birthday is late in December, so when it came time that I was eligible to be enrolled in kindergarten--4 years old, but would be turning 5 before the new year, though barely--my mother decided to keep me home until the next year, and work with me and prepare me for school herself. This turned out to be the best decision she could have made. When I went to school the next year at 5 years old (turning 6 halfway through the year) I was prepared, able to pay attention, eager and ready to learn, and had an easier time than many of my classmates. In fact, I believe this set the stage for the rest of my education: I got straight A's throughout school my entire life, was in the National Honor Society in high school, was always in special classes like Gifted and Talented, and received a full college scholarship. I'm not saying this to brag, only to point out that one year can make all the difference in the world. You know your child better than anybody, and if you feel she would benefit from staying home an extra year to prepare for school, then you should follow your instincts.
Incidentally, growing up, my next door neighbor had a son who was younger than me, and she sent him to school at the same time as me, so that he was only 4 when he started, and he ended up having behavioral problems during school for many years, and never did very well academically.
Obviously, these are both individual cases, but I feel that you should do what you think is best for your child in the long run.