I don't have a room yet, but yes i gasp when i am doing a project.Cus is a mess. I do have a very good motivation tool to keep everything nice and tidy when i am not quilting...An 18 month old whirlwind. If it is out ( i sew in my living room, and cut in my kitchen) he is going to check it out..and run off with it. I don't know how many scraps of fabric i have found in his toy box...
You SIL should have been respectful about your space. If she doesn't like how you keep your stuff, well her loss, not yours.