You have to look at each child individually and decide what is best at the time. This feels right for her so go with it. My dd1 is a feb baby and turned 5 at the start of her first year at school, some kids in her class are over a year older than her, some the year below her are older than her so there is a big spread. The older grades are composites at our school anyway so she always has kids older and younger than her in her classes.