Has anyone encountered your LO doing the opposite thing as was asked?

I don't know if this applies to all kinds of dementia or not, but in Lewy Body Dementia, instructions about physical movement often result in the opposite being done. "Lean toward me" might result in my husband leaning away! "You can let go of the armrest now" resulted in a death grip on it. My son had a much easier time helping his dad stand up. I watched to see how he did it. He didn't say "lean toward me" he said "give me a hug, Dad" and his dad automatically leaned forward into a hugging position.

So instead of saying "Stop biting me" maybe saying "can you stick out your tongue?" would work better. Even if she pulled her tongue in, she'd have to open her teeth!

Thank you...good to know, mom bit down so hard on my finger and when I asked her to stop she bit harder. Lesson learned, don't put my fingers in her mouth. Just trying to help her with her false teeth.

Yes, this is part of the disease. demonstrating what yo want them to do can help. 'Mom. put your tongue out like this'! It's not 100 % guaranteed but it often helps. My Mom would forget how to walk! So I echoed the PTs instructions and said, OK left foot first (and did that myself) now your right, etc.
Also, call them by name before giving an instruction.  Look them in the eye and state briefly, what you want them to do.  No compound sentences, just clear sentences.