I was dying my hair random red colours from about 15 onwards. Dying your whole head blonde may well look a bit naff and I would consider that highlights would be better done properly at the hairdressers... the added advantage is this can be expensive, she'll have to save for it and all the effort will force her to consider if it's really worth it :c)
n awful lot of young women wear different hair colours these days EB, pink, red blue and so on. I think I must be terribly old fashioned, my step daughter has just done her hair and she has just turned 13 . I was flabbergasted.
I allowed my eldest daughter to have blond highlights at 14 -lots of fine blond highlights rather than a 'bleach blond' can look really nice and natural. I think 12 would be ok if it was done carefully and nicely.
Well I dyed my hair Duracell orange when I was 15 so I don't suppose I could be too much of a hypocrite, fortunately the kid's school takes a very dim view of dying hair so I'm covered on tha score ;)
if it's a home dye kit, too many things can go wrong, if it's a reputable hairdressers then perhaps, but quite honestly 13 is still young, and the schools these days don't always look kindly on matters of hair and dye...
As a parent, I'd be mortified if my 13 year old say she wanted to go "beach blonde". I'd question why... and it's probably for the wrong reasons. Boys!