Have your friend do her own cat a favour and build it a simple enclosure outside a window. It will be safe from traffic, bully cats, dogs, etc. It doesn't cost much if you use plain boards and chicken wire to build a "box" then butt it up against the house and attach with screws or nails. Our cats have used one for years, even have a "balcony" (horizontal board) on which they step out and sit, or climb down a slanted board to the grass. I did this, originally, with cats which had been let to run on the prairie in WY, with an open window, free range. We moved back East and they knew nothing about traffic, so they instantly became inside cats.

It also saves birds if you confine them. I heard some story on NPR the other day in which they claimed a gazillion songbirds are killed every year by cats. One state legislator wanted to give hunters rights to kill loose cats. Thankfully he was unsuccessful, but as a cat owner one who is owned by cats I do like the fact that I contain my kitties and keep them and the birds safe.