Dad has type 2 diabetes, has been in the hospital twice within 2 weeks, had a stroke which he fully recovered from but mom is refusing to give him care. She hasn't picked up his meds in 6 months, won't get a test kit to test his blood sugar, gives him candy and high sugar foods, refused the ambulance to take him to the hospital after he had a stroke when his sugar was at 600. Their Dr. is furious. At their last appointment he told her she is incapable of caring for herself or him. His sugar was back to 600 and he was very lethargic barely awake. Dr. suggested assisted living. She refused. He then strongly suggested a home health care nurse to provide their meds every day and test his sugar. She reluctantly agreed. After the nurse came for the interview she told mom she can refuse the care if she doesn't want it! She did. The nurse called the Dr. and he is 1000% behind helping dad. How can she refuse? Isn't that an abusive caregiver? What options are out there?
I once, when very angry, pointed out to her that if she'd taken even the slightest notice my father might have received life-saving treatment before he dropped dead on a squash court at 71. I apologised immediately, because what I'd said to her was cruel and pointless. But the reason it was so cruel is that it was also true.
Stop wishing that your mother would turn into a capable, willing nurse. Are you geographically close enough to supervise their care? What did their doctor mean when he told your mother that she was not able to look after herself, either? - what are her medical/care needs?
When it comes to diabetes, it is a complex illness, so your Mom may find it too confusing to understand, so she sweeps it under the rug. Thus if she ignores this, maybe it will go away.
My own Mom I believe was still under the impression that my Dad was still in his 40's instead of being in his 90's. She would still do a "honey-do" list for him which would include climbing ladders and doing electrical work. Dad use to be able to do those things quickly but no longer at his age.
One time my Dad fell on his driveway and got a huge bump on his head. Mom thought an ice pack and a good lunch would do the trick. Once I found out about the fall, noticed that Dad was too wobbly to take him to urgent care, I called 911.
Have you considered a call to Adult Protective Services?
Is mom mentally ill, or does she have dementia?
This is so tragic. I take it that this was not a functional marriage before Dad got so ill?