When Lyn and I Skyped recently, she noticed that I was wearing something sleeveless. She started to stand and turned to Mom. "I need to go change." Mom and I were both confused. The conversation had just started and it was clear that she was in clean clothes.
"Why?" Mom asked.
"I need to change my shirt." She reached up and pulled at her shoulders as she stumbled around trying to explain.
I realized she thought I was wearing a sleeveless shirt which she sometimes wears around the house. I stood up and got her attention. "I'm not wearing a shirt. I'm wearing a dress." I pulled at it a bit so she could see that it was a lot longer than her shirt would be.
"Oh." She sat back down, looking disappointed.
The power of suggestion is so strong with her you don't even need words.