Hello Friend, Good that you are seeking a help here. As body and mind are interlinked depression can be caused even by physical illness, distress, worry about health etc and visa versa.
Be positive. She can go through a counseling session to first open up to discuss any emotional disturbance that is bothering her.
There are few self therapies, lifestyle routines change, dietary, excersise etc that can help her to overcome such depressive.
Next Steps
Feel free to reach out to me directly or online for further evaluation and suitable recommendation. Be positive. She will be alright soon.