No experience of this school but DD changed to Sixth form of boys' school (though from a predomiantely male co-ed).
With hind-sight not sure a change at 6th form is good idea if they are happy where they are. (We had very specific reasons). AS grades are important & they dont have much time to adjust before first set of modules.
Experience of 'boys'' schools taking girls is that the ethos may not have adjusted to suit females. Staff may have plenty of experience with boys but girls are different
presumably its the hormones
Seriously - it is a wide generalisation but especially coming from a girls only environment DD may find it difficult to adjust to teaching styles/communication with staff...
Also may be little in way of games provision - even practical things like toilets!(Not joking -my DD has found provision very primative!)
Its not just about your DD adjusting (mine is used to having male friends & is strong personality, independently minded etc..) but also the attitude of boys who are not used to girls.
There are the advatages of co-ed but personal view is that this is more beneficial if its from Year 7 & not much difference bewteen year 12 & university from that perspective. Could get same benefits from joining co-ed groups like DofE, orchestra, athletics club.. anywhere they get to meet boys as 'friends'.
If you are going to check out the school I would advise asking some searching questions about how they have dealt with different requirements of girls. The PC answer maybe that there is no difference but I would want to hear that they recognise it may be necessary to adjust the way they communicate to girls & to control boys' 'showing off' in lessons.
Be interesting to hear from them why they introduced girls into the 6th form & what advantages they think there are to the girls (not just the school & the boys!)
Also find out how much responsibilty the girls are given. If the boys have been there for 5 years & are known to staff do they get given all the 'posts of responsibilty' before the girls have a chance to 'make their mark'? If interested in music - do the boys already have places in eg orchestra - how easy for girls to be admitted.
I dont know what we would decide if faced with the choice again - as I said there were additional factors in our case - but if DD ishappy where she is & it is simply a case of the attraction of co-ed I would say don't!