Hi, I'd like to help you with your question.
It sounds like your mother has either had a severe anxiety reaction or she has Post Traumatic Stress disorder (PTSD).
Your mother has experienced some very dramatic stressors in her life with the past 6 months. She experienced the death of her sister, her husband became ill and has not quickly recovered and she got hurt and was handicapped for a while. All of these things have either been about death or illness. The stress of trying to cope with it all has tapped all of her resources emotionally. Her ability to respond to the stressors has become depleted so she is reacting by giving in and fearing the worst.
From your description of her symptoms, I doubt your mother has PTSD. She would be having nightmares, flashbacks, avoiding all things that remind her of her sister or your father, and be agitated. Although she may have some of the symptoms, she does not appear to have enough for diagnosis.
But it does sound like she has developed an anxiety disorder. Excessive worrying, fears of death or preoccupation with death, inability to relax, appetite changes and feeling overwhelmed by her thoughts are all symptoms of anxiety. Also, she may not have had time to mourn her sister's passing, which will cause her to feel preoccupied with death and the sorrow of death. She needs time to work through the stages of grief and time to heal.
Could her doctor call in a prescription for a mild anti anxiety medication? Ativan is an example of a anti anxiety medication. It can be taken as needed (PRN) or on a prescribed basis. It will help your mother relax and rest until she can get further help.
I highly recommend she sees a therapist when she feels better. She can talk to her doctor about a referral or search on line at http://www.bacp.co.uk/ or http://www.cpdirectory.com/cgi-bin/index.pl. Talking about how she feels will help her find better ways to cope and reassure her that she is very normal.
Here are some other resources to help:
Overwhelmed: Coping with Life's Ups and Downs by Nancy K. Schlossberg
The Mourning Handbook: The Most Comprehensive Resource Offering Practical and Compassionate Advice on Coping with All Aspects of Death and Dying by Helen Fitzgerald- when she feels ready to cope with her sister's death
The Mindful Way through Anxiety: Break Free from Chronic Worry and Reclaim Your Life by Susan M. Orsillo PhD, Lizabeth Roemer PhD and Zindel V. Segal PhD
You can find these books on Amazon.com or your local library may have them for you.
I hope this has helped you,