I dont agree, thats not maggies mother in the dinner. If you watch clousely the figure of frankie in the dinner is blur, and this is why: Frankie committed suicide. Just before he is going to the hospital to give maggie her last shot, he is seen preparing a bag with two shots. right at that momment scrap enters and gives him his last talk about freeing maggie from her anguish. The part of the dinner is just simbolic, showing that frankie had at last found peace. And when he talks to maggie about the two of them retreiving to a cabin to be by themselves, is also a symbolism of the suicide, she died and then he joined her.