Lyn has no remaining mental flexibility.
If she gets angry, she'll rage for hours on high, circling repeat. It can be a small offense that sets her off. It could be as small as finding green chile on her donut cheeseburger.
My office mate would point out that her holding a grudge is a family trait given my muttering "water!" like a curse over a mismate drink last week. I may have grumbled but I didn't rage and Lyn's filter is permanently broken. She's unable to differentiate from the small grievances and the great offenses.
Mom tries to redirect her but Lyn's tenacity doesn't give up. I feel for Mom and wish I could change it for her.