The two schools are quite different propositions - one is a big academic school and the other a much smaller, more nurturing and less academic school. They suit different children - what do you think is right for your child?
If you accept the Surrey Hills place, then there seems very little incentive for them to offer you an RGS place.
I assume you are aware of the history but in case not..
RGS took over Box Hill (now Surrey Hills) given its difficult financial position. The idea is to funnel the children from the feeder preps (RSM, Micklefield and Chinthurst) who don’t make the academic level required for RGS to Surrey Hills. They’ve obviously decided to extend that out RGS applicants too.
This is trickier than it might sound though given that Dunottar has traditionally served that market in Reigate (with better results/reputation/location near the feeder schools than Surrey Hills).
So RGS is super keen to make the Surrey Hills move a success. They got their fingers burnt when they bought Dunottar c15 years ago and then sold it on again. Your daughter would be part of the first few cohorts going through Surrey Hills as RGS try to turn it around - there will be pros and cons to that - how does that feel to you?
Can you try and arrange to go and visit again before you have to make a decision? Given the background, you are in a strong position to ask the Surrey Hills for more information/visits/answering of questions if you need it to make a decision. I would push hard for this - you applied for one school and have been offered another.