Poor you and poor Mushroom! I'm afraid my only suggestion would be not to let Mushroom outside anymore (once you get her back home). I'm in the "Cats Indoors Only" camp, though, so someone else might have different advice. Especially since Mushroom was injured once before, during one of her adventures outdoors, I would think it'd be best to keep her inside from now on. But she probably won't like being kept indoors, since she's used to being able to go where and when she pleases. I would also suggest not letting anyone else's cats into your apartment. I don't know how easy it is for them to get in. Do you have a cat door they walk through?