What if, indeed? That's exactly my point, instead of saying "figure it out" the family member should explicitly say what he can and can't do, and help out any way that is needed.

Saying "that's not my problem, figure it out" to some low wage screener (have you ever TALKED to these guys??? they are universally not the sharpest tacks) or expecting him / her to magically know what grandma is capable of, is ridiculous. I'm a doctor, and sometimes people surprise me with what they can or can't do -- the screener is not going to know how to coach a person with Alzheimers disease -- the aide / family member might have much more experience with that. The screener has no idea what is wrong with her.

I wasn't there, so I can't say exactly what went on. But as a general rule, it would be better to offer to help grandma raise her arm, or tell the screener he/she is hard of hearing or incapable of the motion, or otherwise helping out, rather than saying "it's your problem, you figure it out."