They can't pass over Triquatra marks (unless they are extreamly powerful). If you draw one on your friend that will work, you can also draw them on post it papers and place them on her bread room door and window.
Yes, something as basic like this works (because your only dealing with shadow demons).
If this isn't reassuring enough for you; You can place salt infront of her window and door. You could also buy religous objects (they do not do anything, but it makes some people feel better. Also demons generally stay away from them because they hate those sort of objects). And if your really worried then you can burn sage and light a white candle.