Sometimes, if a kitten has been taken away from its mum too young, or has perhaps been orphaned, it has trouble learning to use a litter tray. When I first got my 2 old ladies, they were very young and had been orphaned and they didn't know about litter trays initially. They used to "go" everywhere! Behind the sofa was a favourite place! Cats like to do their "business" somewhere private, so can I suggest that your friend maybe puts puss's tray in the place where he/she is using mostly? Hopefully that's not behind the sofa or next to the bed!! The wee cat will soon get the hang of what's expected and your vet has given good advice. Your friend just has to be patient - it'll get there in the end, as cats are very fastidious and like to poo in their own special place. When my little stray had her kittens, she taught all of them to use a litter tray almost as soon as their eyes were open. Oh, and another thing - cats don't like dirty litter, so keep it clean for her. I find "Beauticat" very good - it's made from pelleted sawdust, smells nice and you only need a little bit, so it's very economical.