Is yelling at a parent elder abuse?

I don't know if I would go so far as calling it abuse unless it was frequent and shaming. We can tell abuse from yelling from what is being said. If your sister is yelling a lot, chances are the stress of the circumstance is more than she can tolerate. What is her role in caring for your father? Why do you think she is feeling so frustrated, beyond not liking the caregivers?

Yelling at a dementia patient isn't useful. They can hear you. They simply aren't living in the same reality. All they hear is the raised voice and they feeled threatened by it.

More details: My sister lives with my dad. My dad has caretakers from an agency. She gets frustrated about the caregivers and sometimes argues with my dad about it. It esculates to yelling. When should the agency report it ?