Spa hotel 15 year old

[Florabella]

I'm looking for a hotel with spa facilities that would be happy with a 15 year old using the sauna etc and would do a facial or other treatment like that for a 15 year old. Would need to be SE England. Any suggestions? Thanks

The Runnymede has a parent and teen half-day spa experience with 4 hours use of the spa facilities plus a treatment.