Indigo, children don't make good progress in the early years, or throughout their school days, for a vast variety of reasons. Establishing why this might be is a good idea, but many children simply mature more slowly than others, and the exceptionally early start to formal schooling in English-speaking countries is a problem for such children, as is the enormous memorisation /rote-learning burden for writing (bed, said, head; blue, shoe, flew through...) Some children will just never be very good at that.
And the thing which makes the biggest difference in most cases is: individual help with reading and writing. This can be a very hard thing for parents to give, but it's hugely worthwhile. You got your dd all kinds of assessments and other help, but the regular help u gave, if u did, probably made the biggest difference of all.
We had to work really hard, regularly, for about 20 minutes a day, for about a year, to help our son with learning to read words like 'said, friend, beautiful, through, thought, people'. I know how hard this is with your own child - without getting anxious, angry or desperate. Sometimes u just have to stop and try again later or another day. And for most of his school days we still just had to accept that his spelling was not good.
We were lucky. By about age 8 he got hooked on reading. He is also bright, never had a problem with maths and in the end learned to spell well enough for his needs. - But some children are not that bright, even if they have bright parents (as I know from being a helper at a club for people with learning difficulties for the past 30 years). They never learn to write well or to score well in SATs. The worst thing that happens to such children is their parents stopping loving them and give up on them because of it. Luckily, most don't.
But I hate the inconsistencies of English spelling more than I can say because they make life for anyone with less than average learning abilities so much harder than need be. They condemn those who learn a bit more slowly than most to learning much less than they could, than their equals can in other languages. - If u want to know more about my views on English spelling, read my blogs. Masha Bell