HI. I am Dr. Jamie. I have a few questions before I answer your question:

1. How long has she been doing this?

2. How old is she?

3. Have there been any recent house hold changes such as a new cat or dog? Or have you changed types of litter or location of the box?

Does here bowel movements look normal?

Where in the house does she like to deficate?

Only on carpet?

Cats can sometimes stop using the litter box if they had a scary or painful experience in the box ( a painful bowel movement, a loud noise while in the box, etc) or they can just have a preference for a certain texture when eliminating. Here are some suggestions:

1.Try the litter additive called Cat Attract (you can buy it online), which is an herbal product designed to return the cat to the box.
2.The litter box length should be at least one and a half times the length of the cat (not including the tail) so that the cat will have adequate space to maneuver and cover her excrement. Some cats like covered boxes and some like uncovered.
3. Try some other type of litter to see if the cat prefers a different brand or type. Sand is a good choice, as most cats prefer something soft. Also try wood shavings, shredded cloth, other brands, etc. Put one type of litter in one box and a different type in another. This often fixes the problem.
4. Put food bowls on the spot your cat is inappropriately going to the bathroom. Cats don't like to relieve themselves where they eat. You can gradually move the bowls to another location when your cat is using the litter box reliably again.
5. Put a deterrent on the area he tends to go. You can cover the area with material that a cat doesn't like to set foot on, such as double-sided tape, aluminum, foil, mats that give off a slight static shock when stepped on - are another option. Also try to spray the area with a scent that cats hate, such as citrus. If your cat uses houseplants for litter boxes, cover the top of the soil with sharp rocks or small pine cones.
6.If nothing seems to work, the cat should be confined in a small area. The cat is gradually allowed more area after he/she has proven that she will use the box.

There is also an anti-anxiety medication your vet may be able to prescribe that sometimes helps.

The sand can be childs sandbox sand from home depot

As silly as it sounds to use, some cats prefer one type of litter to defecate in and one to urinate in. It sounds like your cat prefers carpet/soft textures.

I would try fine grain sand and soft wood shavings in the box and maybe lock her in the bathroom (with no rugs) until she starts using the box again.

You could also try putting down plastic (a tarp?) temporarily in the hall way to break the habit.

Yes, keep the litter the same in one box.

It wouldn't hurt to have them check for parasites in her stool, but usually this will result in diarrhea/blood in the stool.

Your welcome and good luck! Please don't forget to press the accept button to close our chat.