My younger brother was born on 1 March and went to school at 5 turning 6 - 33 years ago. It was the best thing for him. Some of the kids in his class were up to 16 months younger than him, as the cut off at that time was 30 June. He is the third child - similar to your daughter, and just wasn't ready for school. If he had gone early, it potentially would have affected him academically and socially. As it was - he didn't learn to read properly until Grade 3 anyway.

My older brother was born on 30 April and started school at 5 turning 6 - 36 years ago. Again, it worked really well.

I'm a May baby and also was 5 turning six. My DS1 is a May baby - I could have applied for special early entry for him, due to his academic ability - but it would have been disastrous socially for him.

I don't think the new baby timing is something that can't be managed. If she prefers to stay home - do it!

My DS1 plays with kids older and younger than him at school, as does DS2. Kids find their own friends regardless of age discrepancy. My bestest girlfriend from school is over a year younger than me. Academically she struggled, but socially was fine. She would have been far better off staying home for that extra year, but her parents sent her anyway. Another girlfriend (March baby) did Year 6 twice, and says it was the best thing she did, academically and socially.