Elderly people should never be stopped flying and no should anyone be stopped based on their physical needs. However the line must be drawn when just at the start of a long oceanic crossing a crew member is physically assaulted. Crew don't sign up for, nor do they get paid anywhere near enough to put up with it.
What happens once you're on the ground is not up to the crew/airline. If the passenger was arrested then that needs to be taken up with the local authorities.
I'm sure she didn't mean to do this, and I sympathise with her somewhat but I think the crew did the right thing. They had no idea of knowing what would happen if they continued.