That is absolutely appalling LDNM.
The going rate here in Bucks is the same as Greenshadow has quoted for Gloucestershire. Materials are usually included in that price, although some tutors may ask parents to buy a few practice papers costing anywhere between £20 - £100 depending on how many different types of test are to be taken.
I am not trying to send you scurrying over to "the other place", but if you look on the main site (not the Forum) there is a Directory of Tutors and many of the people listed there quote their hourly rate. That might give you an idea of whether this person is charging a fair rate or not for your area.
Regardless of that, the hours are ridiculously high for any area of the country, even for the Kent "super-selectives". In Bucks a standard would be around 25 - 30 hours from January to September. And with a 40 minute journey either way (which you have to do 4 times, remember, unless you are going to sit around for 2.5 hours) this is going to become a huge millstone around your and your DC's neck.
And that statement that "tutoring can only add 5 marks"! That is complete hokum and was disproved by research done in Northern Ireland 9 years ago that found (and I quote) "the effect of sustained coaching over a period of 9 months is shown to be substantial." If all she reckons that she can add for that huge amount of time and money is 5 marks she should be ashamed of herself.
And now she has a queue of children awaiting a slot? And now you have to make a decision by tomorrow? You know those double-glazing salesmen who come round to your house and won't leave until they have your signature on the contract? ...
My opinion: A rip-off merchant. Shop elsewhere.