It will partly depend on your area and whether you are looking at the superselectives.
In year 3 I would concentrate on reading; this is the key to comprehension and VR.
I would also ensure that she is confident in her multiplication & division tables and number bonds.
She also needs to read widely (both fact and fiction) and highlighting any words she is not familiar with.
And did I mention reading......?
We didn't start until the Christmas of year 5 and are waiting for the results now. My younger child (currently in year 4) will start about the same time, but we only need a pass and mine are both avid readers (punishment is removing their books