@mattk56 My sister had a craniotomy for glioblastoma this spring, followed by radiation as well and her memory is completely messed up. I'm her caregiver and a couple things that helped me have been:
1. Reminding myself that I'm never angry AT her. I am angry AT cancer. I'm allowed to be enraged at cancer in a way I would never allow myself to be angry at my sister. That little shift let me process the anger without feeling guilty.

2. My therapist helped me realize that I react so strongly to her memory lapses because it frightens me. It's an undeniable reminder of what has happened and what is coming. It's a fear based response. I'm not a "bad person" for losing my patience. I'm a frightened and sad person.

3. My friends are so important for processing grief! They let me vent, be angry, cry, make the inappropriate jokes that help me cope with the insanity of it all.

4. I'll go to the thrift shop, buy $5 worth of plates or glasses, put on some safety googles, put the dishes in ziplock bags, and then smash them with a hammer to vent my anger. There is something deeply satisfying about physically getting the rage out. Breaking glass is so cathartic. It's like it resets by goodwill and patience.

Hope you find support and relief. This disease freaking sucks!