Agree with lakings1900 - read, read and read some more. Neither of mine are into reading, so with DS2 I read to him every night when he was in the bath and we discussed any words he didn’t understand. We did start to write them down along with their meanings, but that only lasted a couple of months
Also, ensure that she knows her times tables inside out and back to front. Time is critical in the test, so they need to be instant in her head (both multiplication and division).
There are a lot of people who tutor from Year 4; personal choice, but I feel it is too early. I would do basics at home if you’re able to - a few 10 minute Bond tests, understanding NVR rotations, patterns etc. so they are not so alien, and then start with a tutor in Y5. Two years of tuition on top of school can be overwhelming for some children, but you know your daughter best.
I can’t advise on the schools you mention as I have 2 boys. However, they were not in sets until Y8 - in Y7 they were taught in their form groups, and these are mixed ability - they are at HGS so scores range from 205 - 240.
You will find a wealth of information on this forum, so good luck with your preparations.