This struck both of us as a wtf moment. She has not been diagnosed with any type of dementia. In fact, other than her knees, she is in pretty good shape.
She does lie to the doctors about how she feels, etc.
Is this typical of something else going on? Lying? Or making up stories? So atypical.
I called my 97-year old mom tonight at 6PM (as I do every night) and she told me she was sitting down to her breakfast. She had napped and slept hard and woke up thinking it was early morning instead of the evening. Could your MIL have had some kind of dream or medication-induced hallucination?