Mom has PTSD, now at 61 she's argumentative and abusive. Is this Alzheimer's?

Mom's mom had Alzheimer's and dementia. I am new to looking up the information about it, but not new to dealing with those who have it.
My dad died of cancer in 2011. His dad was an alcoholic and dad had his own issues.
My nanny (mom's mom) accused me of stealing.. we argued terribly... she accused me of stealing her clothes and putting them in the wall in my closet. She put cole-slaw in her dresser drawers, ate it later and got food poisoning. I took care of her, because I was upstairs with her, mom and dad was downstairs, and then nanny accused me of poisoning her and said she'd call the police on me.
Well, nanny died in 2005.
Oh my god, so much has gone on.
I'm almost 33, disabled (degenerative disc disease, spinal stenosis, PTSD, psychosis, severe depression, ex-self mutilator). I'm so embarrassed to say this. But.. anyway, mom has obvious PTSD, though not diagnosed. She goes over the past like we're in an eternal time loop, every day, 24/7/365. The past 2 years she's been doing and saying strange things, even thinking my nephew was the one (in a memory of the past) who did something when it was ME as a child, before my nephew was here! She's now 100% violently abusively arguementive. She said something so hurtful to me in midst of argument ("G-D your soul to H*ll!!!!") I was like WOW!!!! She is scaring me. And now she refuses to talk to me or spend time with me. We used to bible study and watch movies together, but now she jokes around about the Bible, curses God, and is a TOTALLY different person. I feel like I don't even know her now. She's 61 years old, and used to worry and roll terrible things over in her mind. I should have known something was wrong when she began, about 5 years ago or so... after dad died, she began to repeat things. Tell me the same things over and over.
What should I do? I'm scared of her. I feel like my heart is hardening toward her.... but I love her so much, and I've always been so close to her that I would have given my life so she could live. That's how much I love her, still.
Help me, please.