Responses
I think she saw shigeru as a danger to her son (which in a way he was, as he was reckless at cliffside TWICE and if she hadn't grabbed him, he would have fallen anyway). She probably felt she had to get rid of the danger (I suspect she got rid of the cat, too.)
Yeah, he had tried to hurt him so she got rid of him. I also think she did the same with the poor cat, which means that she has reached an extreme level of overprotectiveness (and it's very scary)
Something's wrong with the mom since the beginning, yet I didn't expect her to do that to her own nephew (⊙…⊙ )
Did she do this just to show to the others that she had been right with how dangerous the cliff is?