We were in a similar position - moving back to the UK from overseas, DS was aged 8 and had been in a bilingual but US-curriculum-based international school, so started at age 5. Also young in year (August birthday).
But when we arrived in the UK he started in a state school in his 'correct' year (year 4), with children who had had a whole year's school more than him - and it was absolutely no problem, apart from handwriting, as he had not yet learned joined-up handwriting and the rest of the class had. It didn't help that he is dyspraxic/has problems with fine motor skills, so his handwriting was always going to be behind anyway.
But academically he soon found his feet, and he is now 15, in year 11, still among the youngest in the year, and already has two GCSEs under his belt (taken aged 14). He would have been bored stiff if he had been held down a year, and would also have stood out a mile as he is tall for his age - he was among the tallest in his correct year at age 8, and would have towered over everyone in the year below.
If you think your daughter is bright (are you generally an academically able family?) and reasonably socially mature, I would resist attempts to hold her down a year as at that age, as I am sure she will catch up very fast.