I am trying to remember the title and find a collection, by identifying short stories that were in it - this one was a short story involving a young lady, a nurse or aide in an old folks home. Her boyfriend's name was Donald, and she was looking forward to seeing him after work.
She was working with an older, larger, disabled woman. She noticed how the woman held her pinky out for most things... The young woman was trying to get through the day, but her headache was overpowering. Ultimately, it turned out to be part of the old woman's plan - she grabbed her arm hard, and after the bright light, etc - the young woman was looking out of the old woman's eyes, in her body. The old woman in the young woman's body leaned in to gloat about having her Donald and life. The young woman in the old woman's body chokes her to death, all the while staring at the outstretched pinky...
Other short stories in the collection included the "Sound Machine" and I believe "Flowers for Algernon".