Facial expression when she gets emotional. That has nothing to do with race.
And no white (or green) women get similar expressions? Why no Wicked Witch of the West comparisons with Michelle? Does Hillary really look anything like that witch?
The problem with using Aunt Esther, even if the comparison has some merit on appearance and is entirely innocent of racism, is that the other thing the two women clearly have in common is race and, further, Aunt Esther comes with a whole baggage train of black stereotypes that come along for the ride, as well as being a fairly unflattering comparison in general . It's like finding a picture of Evita Peron with a similar expression to one in a picture of Sarah Palin and posting them side-by-side. Perhaps the expression is similar but the other woman comes with a lot of baggage.
As for the argument that both Aunt Esther and Michelle Obama are "angry women" (I'll ignore the "angry black women" angle for now), the general public is not convinced that Michelle Obama is an angry woman, so that leaves them seeing only one comparison. Both women are black.