They forget she has the Force sometimes.

Since Luke left, vanished gods-knew-where, they forget she was his sister. Twin sister, no less. The Force is strong in her family; why, then, should it not be strong in her?

She has some small amount of training, gleaned in bits and pieces from her brother and son. She knows enough to be dead accurate with a blaster, to sense another nearby Force user, to fight with a lightsaber if she truly has to.

When they inform her, with somber mien, of her old husband's death, they are telling her what she already knows.