Arty ... hmmm.
If you are religious, Greycoats is well known, and have an arty entrance requirement, as do Marylebone School for Girls. So I'm guessing they value arty. As others have said, you'd have to be fairly close. I've heard of girls being offered places from further afield (eg. Hackney) in year 8, but it's a bumpy ride.
The Anglo-European in Ingatestone is liberal, though I really don't know how that works out with art specifically, but it might suit because it does seem to promote an ethos of tolerance and respect. And it seems friendly. I think I know of children in Leytonstone who attend it, so perhaps you've crossed it off your list already?
Art at Graveney (Tooting) seems to be very good, but it's a large school, and I wonder if it's as pastoral as you need. It's well-regarded academically, and OK for a London school, but i do wonder if it's a bit "sink or swim" just because of the size. That said, the music department is amazing, and a little school within a school. So if she's musical, she would be fine.
Acland Burghley, (Camden way) though I know almost nothing about it, seems to be very good at taking children after previous bullying experiences, and glueing them back together.
Fortismere is famous. And liberal. Many, many people consider it to be the (London) school at the end of the rainbow.
Mossbourne (Hackney) is very strict, but wouldn't permit bullying. But there are rumours that the head is maybe going to leave, which might change everything ... . Personally, I'm not sure about it, but many like it.
Pastoral is tricky, because you're often then looking for smaller schools, or church schools. And I know this isn't helpful, but it would really help you if you could visit the schools in question. After all, one person's definition of "good" is another's definition of "hideous". You will have to move closer to some of these schools to be sure of a place, and that's a bit worrying, if you're doing it "sight unseen". Though you don't have to be anywhere near as close as if you were applying for year 7 entry.
Can I really recommend you chat to kidscape? And good luck.