She also thinks this would be simpler than attempting to make draperies. Drop sheets foe painting are cheap and work well. These can be found at hardware stores. Various guages of plastic are available at builders' supply stores. The sheeting can be held in place with push pins and sealed if you like with masking tape.
Blankets are also helpful.
Version I is to take sheet of plastic and tape it around the windows leaving the top open. Fill the empty space between the window and the plastic with white dumpster dived styrofoam packing peanuts. Tape up the top. Clear plastic with peanuts gives you a translucent window. Black plastic gives you total blackout.