I guess she wants to draw back a nub. (Image via video still) I don't have the full story of what is happening here, but I would bet money that a white lady was slow to get off an aircraft and was resentful when a Black lady behind her wanted to go ahead and deplane.
So she adamantly refused access to the aisle with her arm. The Black lady was patient momentarily, but when no movement was forthcoming she moved the white lady's arm forward — it's how the elbow works! — and the white lady screamed like she was being skinned a-l-i-v-e.
The best part is when the flight attendant whips out Rosie Perez realness, avoiding going too far but making it clear that this cow needs to shut up and move on to greener pastures.