Declining little by little

I am so frustrated. Why can't our most intelligent doctors in the world cure this awful disease? We live in  the most medically advanced country in the world, and there still is no cure for Alzheimer's. WHY NOT?
I see Mom decline a little every day and there's nothing I can do about it. Now she can't tell toothpaste from hand lotion. Most mornings, she must ask me how to take a pill. She can't remember a conversation from the time she hangs up the phone until she tries to tell me about it seconds later.
I see her get so frustrated because she can't communicate with me she starts crying. And cries and cries until her eyes are red and puffy. My "old" Mom never cried like this.
And yet this is the new norm.
Almost every night right after supper, Mom cries. When I ask her what's wrong, she can't tell me, or says she doesn't know. It breaks my heart to see her like this. I want to comfort her and I don't know how.
And yet, just when I think I've lost Mom completely, she says something that my "old" Mom would say.
I was feeling really bad about Martha not letting me help plan her birthday party and Mom came up to me, patted me on the shoulder and said, "Sally, there's no one with a bigger heart than you. You would do anything for anybody." I was so touched, I almost cried, but instead I said, "Thank you, Mom."
I had a good day today because I got out of the house on a bright, sunny, although chilly, day. I bought flowers that will bloom this spring and summer and even a pink jasmine plant. And while I was shopping I realized I didn't need to hurry because a friend was with Mom.
But then I came home to the same old crap. Mom started going through the mail and I asked her what she was doing as she opened an envelope. She replied she was opening her mail. I asked her to not move it off the table until I had a look at it and she became indignant and reminded me that after all, it was her mail. I told her I understood it was her mail, but I paid her bills now and I didn't want any bills misplaced. Then she started crying, which made me feel guilty. And she left the room.
I had to leave the room too, because I just can't take this at times. Even though I had a break this afternoon, I don't feel like it. I hear all these voices in my head saying I should be ashamed of myself for not being more patient and to just work around these situations. But I'm tired. I am so damned tired. And yet, when I try to go to sleep at night, I can't. I worry about Mom and what the future holds. I worry about money and if we can get along. I worry so much that I'm not getting to sleep much before midnight.
I know I must trust in God because He is taking care of us. He has already seen us through some very tough times and I know He will carry me through all this.
It's just that I get so frustrated because I can't physically make this better. I can't take her to the doctor who will give her a shot and, "Poof!" the Alzheimer's is gone. It's not the flu, it's not a cold, it's not that simple.
God help me and those folks who have Alzheimer's. Pray for a cure.