Hi, She seems to be suffering from Depression. In my opinion, if she is talking about worthlessness of life, there are chances that she might be having suicidal thoughts and ideas.
You can yourslf ask about this. Ask about her feelings towards life. If she admits any suicidal thoughts then urgently you must take her to psychiatrist and get her treated.
Treatment of depression is effective and available easily. Don't delay in getting it.
Once she will receive drugs, she will improve within a time duration of 20 to 30 days and then get her to counselor or CBT specialist. Psychotherapy is needed.