Two days ago, I took in a kitten that was meowing outside my window. I fed her well and she quickly adapted to my household which contains three other, older cats and a sick dog.
No problems there. By yesterday, they were all good buddies. My problem is that she will not use a litter box and has chosen a spot on the den floor on which to urinate. Where she defecates, I have no idea! Actually my husband picked up what he thought was a hair ball, same room, different spot.
I am quietly going crazy! In the thirty plus years I have had cats, I have NEVER had a cat or kitten that would not use a litter box. Any help will be greatly appreciated because the kitten will have to go if I cannot change her behavior.:( :(

Try using the treat for work method where you show the kitty where to urinate and if it doesn't, just hold the kitty to the mess it made and tell it is bad and give a treat to another cat in front of this cat when it urinate in the right spot. This would make the cat want food too. So it will learn next time. I am not sure this will work, but it's worth a try.

How many litter boxes do you have? If there are three established cats using the current ones, the kitten may very well not want to invade their territory to use them. Adding another box in a different area may very well fix the problem. Also, since this is a kitten, it's just generally a good idea to have a few extra boxes around the house, since a kitten often doesn't realize it needs to go until right before it does, so it doesn't have time to go to the box if it's on the other end of the house.