When cats pee or poop in the sink or tub it is almost always a sign of physical illness. Please take the cat to the vet ASAP and carefully describe the behavior to the vet so she will know what to look for.
AFTER you return from the vet, you can try clicking here
to help solve the problem. But, please, please, please take your cat to the vet before you try any of the suggestions on this link.