Cat scratching near litter tray

Question

Before my cat goes into the litter tray to defecate, she goes to the other side of the room and scratches the plastic mat her sisters food is on. I know thios is a sign she needs a pooh !!! Eventually she goes in the litter tray, but keeps knocking food and water over. She is 7 and has never had a problem , until one day a few weeks ago i was cleaning her tray out and she just peed on a pile of clothes on the floor (obviously cos she couldnt get there). The bit of urine that went onto the carpet was removed with Simple Solutions cleaner, and now covered with a peice of wood just in case !!!!! Now whenever she wants a wee she goes to the spot she wee'd on the clothes first and whenever a pooh she always scratches the plastic mat her sisters food is on, but always uses the tray after. Any ideas? It is driving me mad.......

Answer 1

u have to get  a larger size than the cat  cuz they do that cuz its box not big enough   i heard it from the pet store  

Answer 2

It could very well be trying to cover her scent from other cats, i have a dog that does it, and my naighbers cat,who hates my dog, does it if my dog has been in her garden.