Very much depends on her - do you think she'd be ready for it?
My DS started when he was 4 and a half, and he definitely wasn't ready. Although he settled easily into reception (because it is really very like playgroup - not much formal learning at all) he had a huge culture shock when he went into Year 1 - much more formal learning and he simply didn't have the concentration skills that you need for that.
Now he's a bit older (5 and 3/4) he's OK - he's learnt how to concentrate, participate and sit still (basically, he's now old enough!)
Girls are often a year or so ahead anyway, so maybe your DD would be ready? What do her playgroup say?
dd turns 4 at end of August and is due to start in September. She is likely to be the youngest and most definitely the smallest in the year. At the school she is likely to attend (private) she'll go full time straight away but the afternoons are more relaxed with swimming, playtime and so on. We could take her out for the afternoons but the school say very few children actually choose to miss out.
Personally I wouldn't want her to miss out Reception as I think it will be an important time socially if not academically, Many of the children will already have attended nursery together.