How do I get my Mother to stop asking where her daughter is when I'm standing right in front of her?

You will not be able to stop it. It is part of dementia, it will not get better, only worse. You need to redirect her get her involved with something else. And I KNOW how hard that is been there done that. I used to tell my mom the same thing about spending nights with friends. What helped in that case is to give her the name of the friend. It was always a childhood friend that mom knew, and liked, and knew the parents as well. Then I would tell her that I would be back first thing in the morning as we have a cookie making date, shopping excursion, something that I knew mom would like to do. Then I would remind her that it is going to be a busy day tomorrow so we had better get some sleep. It did not work all the time, but quite often.

Swpaula, that is heartbreaking. I think you are on the right track. You certainly aren't going to convince her that you are her daughter -- how could she have a daughter as old as you? She is apparently thinking of herself as a young mother.Sigh.

Can you reminisce about something funny or pleasant that happened when you were young? Refer to yourself by your name. "Paula told me about the time you all went to the beach, and nobody remembered the bug spray ... I know Paula really loves you very much."