claire, the first thing to say is that year 10 seems to be a difficult year for many teens - you're not alone in struggling with your DC's attitude and behaviour at this age.
I have a few questions after reading your post, because I can't quite work out what the problem is... I do understand that this might be because you can't quite work out what it is yet, either
:)
You say the problem is your daughter's 'attitude to school' - but you also talk about her self harming. Do you think she has problems beyond/outside school too? If so, can you say a bit more about these please...
Her cutting/self-harming is the most obvious worry... But are there other things that seriously concern you?
When you say 'she has been cutting', what do you mean? How often, what with, how deep and has any medical treatment been required? (Not that any amount of cutting is to be ignored, of course, but there are degrees of seriousness, and very many young people do it once or twice in a minor way...) What has she told you and what have you seen for yourself?
You say the problems started/her attitude changed at the beginning of the school year, but that you thought she had turned a corner this term. Does that mean she only seemed to be having problems during the autumn term - i.e. Sept-Christmas? Or were there also problems in previous years?
Has something happened to her, or do you suspect that something might have happened?
Has anything happened to you that might have affected your DD?
I'm not sure what to say without knowing the answer to these questions - at the moment it feels like there are bits of the jigsaw missing. I don't want to give 'general' advice (like letting school deal with attitude to school, for instance, and just waiting for a year or two to pass) if there is a more serious underlying problem...
It sounds like, whatever the situation, the two of you could benefit from spending some time with each other right now - whether that's talking formally in some kind of family therapy or just 'hanging out'.
If you can tell us more, I'll respond as helpfully as I can... :)