I'm sorry that no-one bothered to answer this important question. I guess the answer is to support her and acknowledge her, without overdoing it, which can appear patronizing. Perhaps she needs a support group or some happy activity in her life? Check in with her each day if you can, even by phone, and let her know you care. That will help on it's own. She has to choose to start thinking positively and choose to be happy though. But with support things can change for her. Best of luck.