I read it WAY back in the late eighties or very early 90s...it was in the guise of those Sweet Valley High books but not one of them.
It was about a teenage girl living in London in the last year of school...as I remember, her Mum wanted her to stay at school and she wanted to be a fashion designer and get a job...she dyes her hair pink...and on the cover was a photograph of a young woman with pink hair dreamily looking into the future...sitting on some grass in the city I think.
And she gets a job in a naff clothing factory as an assistant...it's run by a foreign man and he gives her a chance and she's making the tea and things but is really happy.
I think the title MAY have had "Summer" in it...