Hi khalsi and welcome to the forum
A Maidenhead girl has just as much chance as anyone else of getting into Kendrick, the school's entrance criteria are about performance, there is no catchment area. I understand from an earlier post that there are eight girls from Maidenhead in the current year 7.
My best advice would be for you to look back through older posts in the Berkshire section and to look at those that relate to Kendrick or Reading boys' school (since threads often contain information about both of these schools). You can also do a search of the forum for 'Kendrick'. I know that there is plenty of advice available about Kendrick because I posted some of it!
I am sure that you will find this website helpful and you can also purchase VR and NVR materials from here once you have identified the ones that you need.
Not sure whether you have also posted in the Bucks section but I would recommend that you do so to find out more about Bucks schools
Wishing you well with your research