Bless you Nana for taking this on and trying to help out your Mom. I am sure that caring for your grandmother has been difficult for her. I truly hate that you needed to find us but so very glad you did. This is a great group that has good ears, strong shoulders, lots of experience, and sometimes even good advice.
What you describe is classic. Your Grandmother is not doing any of this intentionally. It is the disease. Grandmother has become dependent on your Mom just like a child is dependent on their Mom. I would say you are probably at one of the very worst parts of this disease. It is when anger, confusion, and distress takes over and Grandmother doesn't know how to handle it. I would suggest that you let the doctor's involved in Grandmother's care know about her angst. There are medications that will help. She might do well on an antidepressant, antipsychotic, or antianxiety medication. There are meds that will calm her down and take the edge off of her anxiety without causing her to sleep all the time. It may take some trial and error to find the right med but it is worth the effort. My mom was the most angry, depressed, combative person around... until the meds. Today I had a delightful visit with her and she laughed and smiled most of the time. Now I can come and go without the tears.
Medication is not for you or your Mom though the benefits will be good for you both. The medication is for your Grandmother. She is in emotional pain not knowing what is going on in the world around her. Just as you give her meds for her heart and other issues, she needs meds for her emotional distress as well.
It is difficult to tell what lies ahead. Each is different. But it will not get better. It will only get worse. Eventually she will need soft finger foods because chewing and using a fork does become difficult. Her fine motor skills will do which prevents the use of utensils or even how to get food to her mouth. Then you may need to feed her puree foods. She will eventually lose the ability to walk by herself and her large muscle control leaves her. She may use a walker for a while and then need a wheel chair. Dad forgets he can't walk so he tends to get up and fall a lot. For a while she will try to hide the incontinence. She may even play with the excrement. But then she will just use the pull ups and have no knowledge of bathrooms and what they are for. As the brain is clouded she will become less and less aware. Eventually the ability to swallow will be affects and at that point you know the end is near.
Each happens in it's own time and is different from each person. Dad has had vascular dementia for 10 years. His decline was very slow until the last 4 months and he has gone rapidly downhill since then. Mom has been diagnosed with ALZ for 3 years and she is much as you describe your grandmother.
As for nursing homes... Depending on your grandmother's situation, if she has no personal property, money, or income then she would qualify for Medicaid and it would pay for her care in a facility. If she did have some assets then that would need to be spent on her care and then Medicare would take over. You need to talk to your Grandmother's physician about the possibilities. Also there is some coverage under Medicare for in home help, at least on a temporary basis, if the doctor prescribes it. So check with Grandmother's physician.
I also suggest you call your local Alzheimer's Association. They have counselors that can guide you thought the process of Medicaid, available facilities, and the help you will need. Our local chapter also has volunteers that will come over and help out occasionally.
So check with the doctor about medication to control Grandmother's emotional distress. Keep making sure Mom gets some time away and hopefully the medication will change what Mom comes back to. Check with the doctor and the Alzheimer's Association on Medicare help or Medicaid help and the possibility of placement in a facility
You are a wonderful daughter!! Keep asking questions and keep venting...