Moving DD from state to private in Y3?

[JimmyJam2019]

DD has not had the best year at her primary school. Her attainment is mixed, her teacher believes she is able but needs a little more attention and time to be confident in say maths strategies, for example, which they are unable to always give. Socially she has a couple of friends and although was quite shy and somewhat immature for her age (she is second youngest in the class) has come out of her shell more recently.
Her cohort has a reasonable number of kids with additional needs (not necessarily all with diagnosis) and the teacher and TA have struggled this year, this would not necessarily change as she moves up the school, so perhaps would never get what she needs.
Throw into the mix the fact that the Head is leaving in the summer, that throws up many unknowns.
We have a great private school in the area we could move her to but fundamentally she does appear happy in school, so we are worried about moving her and upsetting her, despite the kids seeming nice and the opportunities, facilities etc being way above her current school. We also live very close to her current school, so she would see it all the time.
I also have my youngest DD to consider, who hasn't started school yet. She may fair better at the state school, should I start her there and see or start in the private school from nursery?
Has anyone been in this situation? Words of wisdom?

I'm planning to move my daughter from state to private to start this September in year 3 . She will then stay in that school for secondary.
My reason is that she needs the extra attention and smaller class size the private school can offer.

I know it will upset her to be separated from her best friend, so I'm trying to get them doing an activity weekly together after school.

If she is happy in the school, have you thought of getting a weekly tutor and then going private for secondary? I found out many dc in my dc state school primary have tutors. I did not realize it seems to be a thing (at least in our school!). I would save the private school for secondary.

How much of a stretch is it for you financially? What if both your DDs end up at private school all the way up to age 18 - is that doable for you?

I moved my ds from state to private at end of year 2, so beginning of year 3. He wasn't unhappy at school but situation sounds similar. He's very quiet and shy and was getting lost in the chaos of 30+ children to be honest! In year 2 his attainment was really starting to slip.

We actually made the decision last minute during the summer holidays and it was the best decision for him, he's very settled and engaged with school and seems very happy. He's becoming more confident slowly and the opportunities he's getting are amazing.