You can only expect demented behavior from one that is demented. She has no idea what you think is important or what you want to keep. She only knows what her mind is telling her in the moment. These are her things and I am sure each holds a long term memory in her head. If she is putting things in a box and not taking them out then she's doing well. I did not take Mom back to her house to clear out her stuff. She was incapable of grasping the reality of what was going on. When we moved her out, she moved around ineffectively picking exactly what she didn't need for the move. She latched on to things that were unimportant and was ready to throw out family treasures. That is just the way the demented brain works.
When you yelled at your Mom about the blinds of course she responded by stopping what she was doing.... and then came up with some explanation. I don't think she truly understood that you had told her in the past not to close the blinds. She was responding to somebody yelling at her in the moment. She will probably do it again tomorrow night. If you yell at her again you will probably get the same response from her. There is a difference between knowing when somebody is upset and knowing WHY somebody is upset. The ability to determine emotions and respond is located in the basal brain stem which is the last affected by dementia. Mom, who can not speak, walk, understand instruction, or eat by herself still knows when I am angry. I can see it on her face. It's a fear response. Your Mom still has the ability to come up with explanation.... my Mom just cries! I don't even have to be angry with her. I have to be careful when I get into a heated discussion with somebody else in her presence! You got what you wanted which was her leaving the blinds alone... but her mind is left with confusion. She probably sat down meekly after giving an explanation. If so you are lucky because many will respond with anger. The docile or anger response is based on their nature, their level of angst, and their mood in the moment.
Yes, I had that same problem with my Dad. He would close the windows, shut the blinds, lock the doors, and make sure the house was secure for the night... OVER and OVER and OVER!!! This could start as early as 6 pm... and continued until he was finally asleep. Sundowning is the condition of heightened confusion at the end of the day. Research has not found an explanation as to why this happens but it does happen. This is a time of heightened anxiety as well because of the extra confusion. Closing up the house gives a sense of security. I just allowed Dad to do what he needed to do in order to find a sense of security. Of all the battles I have had with Mom and Dad over the last 15 years (Dad's Vascular Dementia from 1998 to 2010 and Mom's Alzheimer's from 2004 to present)... this was not one I wanted to wage
What you need most is somebody that will give you a break from Mom. Please consider an in home care giver or sending Mom to an adult day care for a few days a week. This will give you time to for yourself and give you time away from Mom to recover. This is not an easy job and it will only get worse.... so please get some help