Usually I never ask anyone to move their camera or anything if they're in front of me. I just get up and move, especially in that Country Bears seating area, there's loads of room to move to. I don't try to get petty and sit in front of them either. I just move to another spot. It takes nothing but a few seconds to move in that specific situation in that attraction.
Now if you're in a Fantasmic situation where there are no seats to move to and the person in front of you has done the same thing... well then I'd be forced to speak up. If the person in front of me in that Fantasmic situation said what that lady had said I'd most likely lean forward and tell her "either you switch places with someone else, lower that screen or stop completely" Give them choices. If they continue to be rude and not put it down or move the thing well then I'd have to call a CM over.
Most times CM are young adults who are not sure what to do when confronted with this type of situation, they can tell someone something but the person in question usually won't listen to a younger CM. So what I usually do is when I complain to a CM about another visitor being rude I tell them that if they feel they can't handle the situation to please get a manager or someone higher ranking to deal with this situation. They usually always grab someone, a lead or someone higher ranking to deal with me and my complaint. Works every time.
Yes you may miss the show or a scene when doing stuff like this but in the end the iPad will no longer be in my way for the rest of the showing.