Poor baby, depression is so awful, I've lived with it since a teen. My DD is 11 and for a while she was a little depressed. Teared up easy, found night times hard, didn't really know why either. It's passed thankfully and I do suspect it was hormonal.
Obviously counselling is absolutely the best idea for her but in the meantime, she is going to need you to help her, which I know you must be doing.
Keep her away from anything negative, such as films, YouTube, news, anything that is basically depressing to read or watch. Encourage her to watch appropriate comedies, cute animal videos, cheerful music. May sound silly but it helps.
Routine, as much as possible. As she isn't eating much, that won't be helping. Cereal bars and breakfast biscuits were my saviours at my worst. She needs to nibble on things little and often. Flavoured water, in a sports bottle, to sip at with lots of enocuragement and reminders.
Take her out for a walk every single day. No ifs or buts. If you have a dog, get her to walk it with you. If not, could you consider a dog? I cannot tell you how much having a dog helps with depression. They provide a comfort, friendship, safety and exercise.
Encourage her to journal. To write down everything that's going on in her head. Get it out on paper so it's not stuck whirling in her head.
If she is crying, let her cry. Crying realeases stress hormones and lowers anxiety. Believe it or not, crying was a sign of recovery for me. I was so severely depressed I was incapable of feeling any emotion, let alone tears.
Try to talk to her again. Or ask someone she really trusts to speak to her. Sometimes children just can't talk to a parent no matter how much they love them. Some children try to protect their parents or worry about hurting their feelings. You need to find if there are any truggers, bullying, boyfriend trouble, friend trouble, worrying about death, self esteem problems. There could be anything.
Most of all, don't show your concern. I mean that in the nicest way. The best thing you can be for her, is her strong mum. She WILL be okay.