Agree with Confidence - it does seem to vary enormously depending on whether you are in an area where a set % (20) get into the grammar system or somewhere where grammars attract 1000s of applicants for 120 places!
But if your daughter is really motivated maybe she will pull a pass out of the bag on the day.
We have had issues with DS doing papers at home and can just tell that his scores fluctuate (although more twixt 60 - 90%) depending on his mood, how tired he is and whether he can be bothered. They are only 10 and really who can expect a 10 year old to always strive for 100% when they are just practising.
It has been repeated several times at some of the super-selectives that we have visited that what they learn in KS2 should essentially be enough for maths and English. Think the Level 5 figure is used as a guideline only - DS and about 1/2 his class are already working to Level 6s (they are a bright class) but still not convinced they will get into the grammars....
A child who is self-motivated under her own steam deserves a place more than a child who is tutored (but not really up to it with natural ability) so good luck. DS has two girls in his class who epitomise this polarity to the nth degree - one has never been above the middle (of five) tables and very flighty but being intensively tutored, the other a lovely confident, well rounded, mature and bright girl with unassuming but very clever parents who is only getting help from her parents. The second girl is just so much what a grammar school should be looking for in candidates and it will be grossly unfair if the former gets a place and the latter doesn't....
Also, just remembered reading on another grammar school threat that one Mumsnetter (also a teacher) said that it is often a surprise as to which children pass and which don't - it is not necessarily the ones that one would expect to do so who do....
When are the 11+ exams she is taking?