I'm currently watching a friend's cat because of some housing issues she's having.

The problem is that Cleo (cat) has chosen to hide in the bathroom on the windowsill. She has her own litter box,food,water, etc. So she doesn't bother the resident cat. I have 2 issues. One is that Cleo hisses at me and my wife whenever we go into the bathroom, and 2). she is flinging litter everywhere from her box.

Does anyone have any ideas how I can help her to calm down some? I know she's stressed out and upset at being away from her family, but this is causing stress for my wife and I too.