The best way is just to ask her if things are getting worse. If she is suffering significantly more than she did before, you should be concerned.
It may be hard for your loved one to be objective about her condition. If she is in denial, she may try to explain away her depression by blaming it on bad luck, life disappointments, or other people, including you. She may tell you that she is just having a normal reaction to bad circumstances and that she has to suffer with her negative thoughts and emotions. However, there is no normal human response that leads to isolation, obsession, incapacity, or suicidality, and there is no excuse for letting someone with unipolar major depression suffer unnecessarily.
If you need more clues to the severity of your loved one’s depression, see if she has lost interest in the activities of her life. Find out if she is refusing to take advantage of supportive resources like her doctor and therapist. Be concerned if she seems to have intrusive thoughts, decreased speech, impaired logic, or confusion. Here are some other signs of worsening unipolar major depression:
• Aloofness and detachment from family and friends
• Preoccupation with death and dying
• Spending too much time alone
• Losing interest in work, school, or home responsibilities
• Increasing frequency of accidents or unnecessary risk taking
• Increasing use of alcohol or drugs
• Poor hygiene, including failing to bathe, brush teeth, or wear clean clothes.
• Decreasing appetite or sleep