Sorry, I meant to answer this but I was busy until today and would have forgotten it if Tracy hadn't given it a nudge.
It's not that long since we went over the relevance of SATS to 11+:
Basically, they're only a general indcation (Bexley and Kent has no relevance at all, by the way - things are very, very different there). If you're getting good SATS predictions then it's encouraging, but no more - level 5s across the board in Y6 (or even Y5) won't guarantee you a KE place, conversely lower levels don't mean it's completely out of the question either.
At start of Y5, 4a/4b is a good place to be (you can expect to go up a couple of sub-levels per year:
The maths is a worry (roughly average for start of Y5) but you've basically already been told that's not an accurate reflection of her ability and you've got plenty of time to work on it anyway. There's nothing in what you've been told that says "don't bother".