How do I help mother through grief of losing my father?

Dad passed eight weeks ago. Mom at first was in a frenzied state getting rid of all dad's things. This greatly upset myself and my sister. Now mom(84) is greatly depressed and chooses to sleep most of day. She complains she cannot sleep at night. She is still eating and has some activity. Mom has a sitter four hours a day to help with many things including showers, meals, etc. Any suggestions how I can walk her through this time? The only hobby mom really has is complaining and causing conflict wherever she can. She has no interest in hobbies. Her personality is very narcissistic. She has been diagnosed with mild dementia and mobility is an issue due to bad knees. Is this anger a new level of dementia or just grief? Her primary care doctor is very aware of her depression but she is already taking enough meds. I have decided to take care of her from a distance somewhat because her constant agitation and anger is focused on me, her primary caregiver. I have reduced face to face visits and shortened the time I am at her apartment. She adores her sitter and enjoys her time with her. I have a 91 year old aunt to care for also and other stressors. I am 64 but still healthy physically. Mom is exhausting.