DD had similar.
Wasn't reading at start of year 1 let alone writing. (Suspect mild dyslexia, but as she has improved we haven't had it formally assessed. Yet.)
End of year 2, 2c for writing, 3b for reading (she started reading for pleasure big style half way through year 2).
Writing has slowly progressed, given time she can write some wonderful stories, but when given a theme and time pressure, she still struggles and primary school didn't really help. They told her to plan her story but never how to in a way that she would.
Her spelling is good when it comes to a spelling test, grammar and punctuation also good, if that's all she in concentrating on. She can write some excellent descriptive sentences. It's just putting them all together.
End Year 6, 5c for writing, 5a/b for reading. So it's sort of caught up. (Not helped by a not so great year 6 teacher tbh)
Seems to be coping at GS so far, but although it's one of her favourite subjects, I'm not sure it will be her best by a long way. (This week it seems she is an ICT geek. Still, worse things to be.)
Unfortunately, as I'm dyslexic and I suspect DH is too, we aren't best placed to help her. I just hope English teaching will serve her better at GS. So far so good.