I can see that this is a really worrying time for you. I am glad that your child is willing to get some help with the difficulties with the drugs. This is one good thing. I am glad that she might be expressing some of the pain and anger that has built up inside as a result of her experiences at school, that is better than holding it all in, I think.
There is nothing like bullying and rejection for lowering the self esteem. But she is just becoming an adult, so there is time to heal and rebuild and strengthen the person within.
She knows that you love her and that when the going gets tough, you are right there beside her.
That's a good starting point.
Then there is keeping safe while on the medication. Talking the side effects over with the prescribing GP might be good. I know it is said many times, but finding the right anti -depressant/ mental health meds can take some time. I know this. Unfortunately it can seem like trial and error.
It takes time to recover from the pain of bullying and rejection, teenagers are really vulnerable as you know.
A good talking terapy can help your child let off steam and come to terms with the past and then face the future with hope. Art as a therapy or Art therapy might be a good idea.
The thing is to brain storm with your child and find things that she might enjoy that will help bring healing and raise her self esteem.
But it is not just about her, it is about healing and recovery for you as well.