Very interesting. My mom has dementia, and I have noticed her sleep is recently very disrupted, and she wakes up in the middle of the night, with nightmares.
I remember a case of a guy with terrible nightmares. He had sleep apnea, and when his breath stopped, his CO2 levels skyrocketed, and it triggered a panic response like drowning, or not being able to breathe. His brain responded to this by creating dreams to match the fear.
She might benefit from a CPAP.