Grieving the living

My mom has Alzheimers. I moved in with her and my dad 2 years ago. At first my dad was taking the brunt of the abuse. She is so mean to him and occasionally hits him. Normally my mom is sweet, conservative, and very religious. Now she is mean, conniving and the complete opposite of who she was. We finally heard of medicine that could help somewhat with cognition and aggression. And for her it seemed to work. It definitely calmed things down. She still fights it every morning but my dad has a way with her that she eventually complies. But my dad is hospitalized right now and it's just her and I. She has viewed me as her adversary ever since I moved in. Mostly accusing me of stealing and taking over her house. There was one physical altercation and I moved out. But 9 months later my dad needed me to come back. But ever since he went into the hospital a week ago, mom has refused her meds and it's been a nightmare. Then the second altercation happened. She threw my phone on the ground while talking to my dad. I scolded her and went into my room and locked the door. She began beating on it and forced it open. I set my phone down to push her out and she grabbed it. I wrestled it away from her so she grabbed her iPad and tried to hit me with it, screaming at me that she should kill me. There was rage in her eyes. The next morning it was if nothing had happened. But I didn't have the benefit of not remembering. If my dad passes away, I will have to care for her alone and I don't know how I can do it without us harming each other. We can't afford a memory care facility. Idk what the F I'm going to do and I'm scared to death. I find myself wishing she would die. It's the harsh truth that I'm not afraid to admit but am ashamed of thinking it. I feel depressed and desperate while mourning the sweet mother I knew while a demon has taken over her mind. She's already dead but still alive and it's agonizing. Why is this happening to her? To my family? I'm mad at God