Forgetfulness, or taking longer to remember something, are normal experiences as we get older. Stress can make it worse. If you are caring for someone with dementia, you might be more keenly aware of those lapses and quick to worry prematurely. 

None of us likes to be told what we can and can’t do. People living with dementia are no different. This activity is something that she identifies as being significant to her quality of life.

Minor memory loss and difficulty learning are common for first-stage Alzheimer's disease. You may also notice a loss of energy and spontaneity, as well as mood swings, confusion, trouble communicating, and difficulty organizing.

This is a very common experience. Sometimes early in their dementia people will have an occasional moment when they forget someone they know is gone, and you can gently nudge that memory  back. 

It can feel so hurtful when people we love say things to us that they never would have in the past.

This is a tough spot to be in. Caregiving is an exhausting and often frustrating job. Your sister sounds like she’s under a lot of stress and needs some resources.  You might be able to offer her an afternoon off, or “gift her” with some reading material (see:  Book Review: The 36-Hour Day – SJL DRC (stjohnsliving.org)  But ultimately, she will need more than that, as time goes on.

First, try to determine why they are getting up. Are they done sleeping and ready to start their day? Or, are they waking because of a need, such as having to go to the bathroom?