What will happen to the furnace if all the vents are shut all the time? My mother with dementia keeps closing them.

My elderly mother still lives alone even if she has dementia. She wants to stay in her own home. She has a nice newer home all paid for. The home has forced air heat with vents in all the rooms. She closes all the vents and then turns the heat up HIGH. When I go to visit her, I have been opening the vents but she caught me doing that and yelled at me. I told her that the furnace would have a problem if she continued to close the vents, but she still yelled at me. Said well its her house and she could do as she pleases. So now I just leave the vents alone and let go and let God. My question is what will happen to the furnace if all the vents are shut all the time? I would hope that the furnace would not blow up, but you never know.