I'm not sure why you'd need this service.
I just looked at their site, which claims:
We have a proven, decade-long track record of significantly increasing the success rates of our applicants. Those making use of our Premier personalised support programme are almost three times as successful as the average Oxbridge applicant.
How on earth do they gauge that? What is an 'average' Oxbridge candidate? I'd ask for clear explanations of how they arrive at these figures.
It may depend how clued-up your school is. If they are not, they can harm an application. A good school will understand what is needed. Perhaps a company like that would give good guidance to someone from a school with no track record of applications.
What sort of school is she at? What's their Oxbridge policy?
There's loads you can do as a parent to support her.
Encourage wide reading or practise around her subject.
Ensure she's on target for A*s in all subjects.
Take her to visit Cambridge to look aorund colleges, departments, to open days and master classes etc so she feels comfortable with the town and knows her way around.
Make sure she has done her research on what papers to expect for the entrance exam, and that she has done practise papers or similar and is scoring well on them.
Above all she needs to know that an active, self-driven passion for her subject, demonstrated through wide knowledge beyond the A level/Bac/Highers syllabus is what they most want, along with aptitude.