hi hkmama, apart from the practicalities that have been discussed etc, thanks for the link to that article which was interesting.
However I find it confuses/mixes up a lot of things (redshirting; countries where traditionally parents have had a lot of choice in school entry year and it is generally a 'stages not ages' thing rather than with competitive advantage in mind; mixed age year groups; skipping ahead/being held back a year) and doesn't really provide evidence for anything at all; at the end of the day it reads like (and this is very common) someone is trying to make a point and gathers evidence to shore it up; but because there is very little evidence (if any), they use even vaguely related things too, to create an impression of having many sources pointing in the same direction.
The data for results by age (Summer/Autumn born) in the UK is very clear; in the early years of school, summer born children are massively less likely to meet standards than autumn born children. Summer born girls compared to Autumn born girls have similar differences in the probability of meeting expectations as summer born boys compared to autumn born boys, though for boys the likelihood is overall lower than for girls. The difference does reduce over time but is still huge at end of Y2 and noticeable at university entry stage. In my opinion this is because the expectations/standards, but also teaching and learning styles, are adapted to the average abilities/developmental stage of the older half of the cohort. Which means that, on average, the younger children will always be struggling to keep up. It's not about being oldest/youngest (someone has got to be the youngest) but rather about (un)realistic age related expectations.
The situation in the UK cannot really be compared to data from any other countries, so the evidence from that article really is quite meaningless for you. When standards are set more towards the younger end of the age cohort, being young in year will have different effects. In mixed-age groups, being young in year will have different effects. Being young in year is not really comparable to being accelerated anyway. When traditionally there is a lot of choice into which cohort a child can go, as in some of the studies cited in that article, then there is likely to be a strong element of self-selection; children that are not 'ready' yet are more likely to be held back compared to same-age children that are, and it is probable that the same reason for them not having been ready yet will explain, in part, their weaker results later on compared to those children that WERE ready; rather than the fact that they were held back. Also most experiences of changing cohorts that you will hear will be from people educated in places/times where changing cohorts is/was common; and thus not really applicable to your situation as it is so very rare in England.
Now this does not really affect you as it is averages and other people's experiences and data from different systems, and you're concerned with your specific situation and indeed it is possible that your daughter might comfortably meet expectations in the year ahead, and be well adapted socially.
But as people have pointed out it is unlikely to be possible anyway. So what I would suggest, also in light of your latest post regarding more 'alternative' provision, is to keep a look out for schools that have mixed-age groups; here you would get the benefits you associate with that without having to go 'out-of-year'. Often these will be small schools, or schools with an intake that is not a multiple of 30. Many people dislike this but like you, I personally do see benefits from mixed-age classes and there is no reason not to choose those schools - many parents do!
But also, you mention that We prefer non-traditional, nurturing, less homework, more emphasis on character and creativity. Now you are much more likely to find this, at any school, in Y1 than in Y2; often people who consider moving their child up a school year do so because they are seeking more formal learning and 'pushing' (often associated with Y2) rather than the more relaxed learning often found in Y1. From this perspective you should be looking at keeping your child back rather than accelerating her! There are of course some rare schools that resist the 'results' pressure and manage to focus on creativity and nurture, but they are hard to find (at least in our region) and I'm jealous of anyone who is lucky enough to have their kids at one.