not using the litterbox sometimes

Question
Hi My grandparents took in a 6 month old female cat that someone did not want anymore. (because she kept pooping where she should not be) She is a happy and loving cat. but about once a week she will poop next to her litter box or in the bath tub. My gandparents tried cleaning out the litter box every day to just a couple times a week, changing litter brands etc. and she still does it. She was taken to the vet and she has no illnesses. What do you think? I would like to solve the problem because when my grandparents pass away (hopefully not for a long time!)this little kitty will come and live with me! I have had many cats and never have had this problem.  Thanks.

Answer
Hi
It sounds as if you have a very insecure kitty there. Cats use faeces as an extreme marker, it sends a bigger more visual message than just urine. Please read my page regarding this problem. Its called middening and is all about territory and feeling insecure.
Here is the page, i hope it will be able to provide some answers for you.
/cat-poo.html

Kate