I guess it depends what you want from 6th form. Certainly, college expects students to grow up, take more responsibility for their learning, there's less hand holding. Some students are not ready for this, but others find this an excellent stepping stone to university. I used to teach at a very 'supportive' school - but every 'free period' the students had was supervised, and as a teacher I had to ensure the A level students worked in silence. Sure it was very high achieving (way beyond anything you'd get in Swindon
) and very supportive but I don't think it did the students any good at all.
I would also say that any college has the benefit of having specialist A level teachers. Therefore, we spend most of our time dealing with Ucas applications and the like so able to give more support about that. Further, I know in my faculty most depts have at least one examiner, and lots of subjects run weekly drop in support classes for students. So no, whilst college lecturers do not know the students, they do have more time and more specialism in the support they offer. (Less pastoral, more academic in my experience). I suspect Ciren would be the same in this.
As for extra curriculars, I would expect colleges to outweigh schools in this (certainly that has been my experience to date, but I've not been in a Swindon school) I know my place offer extra curricular opportunities in music, lamda, yoga, sport, creative writing, pre driving, debating, trips to Kenya, you name it, there's something on offer - that's one of the major benefits of having large concentrations of similar aged students.
On an aside, if your DD is musical but not keeping it up, but wants to - has she considered doing an EPQ? Some Russell group unis (Southampton / Warwick) give students a reduced university offer if they do well in the EPQ. It can be a good way to keep up a passion and get something for it. However, be aware other unis are only interested in them if they are directly related to the degree (in the interests of being impartial).