Wouldn't the mother's body be going through nicotine withdrawal?
They made a point of showing us that Ellen, the mother, smokes. But when she switches bodies with her daughter, Annabel, the mother's body should still have some kind of craving for nicotine. Even if the new "ellen", as annabel, doesn't smoke, at least she'd have a weird feeling throughout the day realizing her mother smokes cigarettes, and that her body needs it.
I found this strange. I just saw this version for the first time tonight, but it was something I picked up on right away.
"Yes, it was very sad when the guy stopped drawing the deer!"