Walls and Ceilings - drywall or plaster- keeps crumbling and won't hold a bracket

My mother recently moved in to a retirement home. The walls are thin with a space of approx. 3" then there is concrete. My understanding is that this was done to reduce flames inn case of a fire. ?? She has sliding glass doors in this area and I have attempted to hang venetian blinds. Each time I do this the bracket pulls loose! I have tried several different kinds of anchors (mpst recently nylon toggle bolts) but nothing is working. :madhell: I have even tried glue but this just pulls the "paper" off. I amd not sure if these walls are plaster or drywall. I'm thinking its plaster. I only know that as I screw something in the wall begins to crumble. It doesn't seem like the drywall I have in my own home. At this point I have several good size holes that I need to repair. (thinking I'll put some spackling on it ???) Someone tried to explain that as I am repairing the area I should tried to install a metal toggle bolt that the spackling wll adhere to- thus making it more likely to hold. At this point I am reduced to putting up a small lightweight rod with a sheer curtain - but the way it is now even that hasn't held. I am darn well not giving up on this until I have exhausted all efforts- this has been such a challenge and I intend to win if possible! :wall: LOL

Please help - making sure to answer in layman/woman-doesn't-know-much about-what-she's-doing terms!! Thanks! :confused: