Aren't you glad YOU aren't a teenager any longer?!
There is probably no real solution to things like this, and any desire for change has to come from within the child (young woman?) herself.
I worked over twenty years in primary schools, mostly as TA, and a few years in secondary. Newton said for every action there is an equal and opposite reaction; he obviously didn't mean it applied to children, of any age, but I think probably "if you push her, she pushes back."
For a start, evaluate what she was like BEFORE moving to secondary. How did she behave, work, socialise at primary school? Was she HAPPY at school, and I mean really happy, not just tolerating it, or struggling to cope? Might the problem have been lurking BEFORE she started secondary? Did she have out of school activities, hobbies, sports etc? If she did then, does she still keep up similar things?
So, as far as is possibly, (in teen-speak) CHILL, COOL IT, try to put a minimum of pressure on her. Children don't WANT to be unhappy, but circumstances and hormones often conspire to prevent them being HAPPY.
A counsellor at school does move the issue onto a more formal basis, so might be a last resort.
What is her work like at school? Does she have excessive 'screen time' at home? Does she 'live' on social networks?
Think about these questions, and if she will, encourage her to talk about them with you. If you want to come back with info, I'll see if I can help further.