We did notice the ten foot fence with climb proof top around the upper directly opposite Becky high when we have dropped the boys there for discos. Last year my son said it reminded him of the boy in the striped pyjamas! I'm sure he was getting the wrong idea and it is genuinely to protect the upper school from being broken into or vandalised, not to keep the upper school boys from becky high girls who should be saving themselves for the grammar boys shipped in on disco day.
Has your daughter got a preference,,sometimes the choice can be down to friendship groups, or even in some cases to divide friendship groups. There has to be a fairly big pull imo to choose a school that is further away, we did and although we don't regret our choice, the extra rather mile up a hill sitting in congestion is a pain in the bum for both the boys and ourselves when we collect after clubs.