What Causes Blackness Around The Eye Post Treatment For Rotovirus Infection?

Hi. I m visiting my mother, I ve been here for about 2 hrs now and I just noticed that she has a black eye. I didn t notice it when I first got here, she said she didn t have one earlier today, what would cause a random black eye, just in the last hr or so? She did have her glasses on for a while about an hr ago while reading and when she took them off is when I noticed it. She did just recover from Rotovirus and was hospitalized 2 weeks ago with severe dehydration, but is almost fully recovered. She is also diabetic.