These schools are very different in many respects.
Tormead consistentlty achieves far better results than Priors Field, at both GCSE and ALevel. Whether that be due to it being better value add or simply more selective, the results are leagues apart.
Priors Field is unashamedly unselective and that will absolutely suit DDs who are less academic but still want all the frills of boarding and/or private school. This is a market place they have always done well in, and fair play to them, the product they offer suits.
Someone above mentioned 'space', and it is true PF has more acherage than TM, and TM is city centre rather than out of town. This will suit people differently and those who don't mind a car journey to drop off at PF for a great rural enviroment should consider it. TM however can also be accessed by car, and there are plenty of transport options for DDs too, give it it's centrally located in Guiildford, also nice for sixth formers, who have guildford town and the pupils of the other two big centre schools to 'hang out with' - yet, no rolling fields.
Do also consider the stability of the school. PF has been around a long time and will hopefully continue to do so, but it is much smaller than TM and has a lot less financial resources. Comparing companies house you can see TM has £5 or £6million in cash reserves, plus is spending on facilities, with a £1.2m surplus for last year, whereas PF has a lot less money and only £200k free surplus.
Also pastoral care is strong at both schools, or at least is the reputation. Go to open events and ask questions to see how deep that actually goes.
Either way good luck for your DD and yes go with your gut, but also your DD must be happy with her choice.