Must say Rishworth aren't very forthcoming on the website!
There is an Entrance Assessment for pupils at 11 years old. This is held in November, December or the early Spring of each academic year.
.. I wonder when the test is???
Many of the independent schools will have similar tests: tend to be reasoning (NVR & VR), english and maths +/- an interview. Some offer a lot of places and many girls taking indie exams end up with a surfeit of places. If you are looking at York there is Queen Margaret's, St Peter's, the Mount, and Bootham. Also Harrogate with the Ladies' College & Ashville. Nearer Leeds / Bradford is Woodhouse Grove. Furtgher afield Giggleswick and Casterton.
I suspect the best advice may be from your daughter's prep - where have they sent girls in the recent past?