I think my mother sometimes thinks I am *her* mother. Any advice?

My mother was diagnosed 8 years ago with vascular dementia. She had a medical crisis last summer and the flu last month, and things are deteriorating. When I took her to the ER for what turned out to be flu (I thought it was stroke, she was literally not speaking sentences and holding her head like it pained her), she told the nurses I was her mother and begged me to 'help' her, (she didn't want them taking blood and it got ugly). It threw me, but I shrugged it off as part of the general stress and delirium of that whole incident. But last weekend when I went to fill her pill strips, she started getting pouty and child like with me (after greeting me in a full on rage of false accusations), and started whining how unfair I'd been to take them to Florida in the winters and never let her play in the snow, and buy winter clothes for her and never let her wear them. I tried to laugh it off, but it really bugs me. Has anyone ever heard of this before?