Pooping problem

I have a 7 year old tabby who has had a pooping outside-the-litterbox problem for years. Her litter box is located in the upstairs guest bathroom and is cleaned every day or every other day. She uses it just fine for pee but will poop on the tile in the bathtub or on the tile floor. Now, she has started pooping in the downstairs den (right in the middle of the carpet). Sometimes she will poop in dining area or even on the guest bed. We've had to put plastic on the bed so she won't go there again (she did it 3 times).

We've made a big stink about cleaning up her messes and yelled at her for doing so.

We thought that maybe her stools are hard and she is constipated: She only eats holistic cat food (dry mixed with wet). We've started soaking her dry food in water to help soften her stools. I've tried pumpkin too.

She is the only cat and doesn't have any competition.

The vet cleared her for any medical problems.

We tried a hormone plug-in for stress in the areas where she likes to hang out.

We've tried re-litter box training by putting her in the guest bathroom for a couple days until she started using the litter box again. As soon as she is let out of the bathroom, she poops on the floor like nothing happened.

Any suggestions???

Oh, and we've tried changing litter brands too. Nothing seems to get through to this cat!

Hopefully someone will come along with more experience than I have, who can help you out but I wanted to offer one suggestion--have you ever tried Dr. Elsey's Cat Attract?  We have an old cat who regularly pooped on the floor.  I used the Dr. Elsey's and it really helped him start using the box--not every time but much more regularly.

Have you tried adding another litter box? Many cats won't defecate in the same place as they urinate. How about covered vs. uncovered boxes? Most cats prefer boxes without any cover, but there are some (like ours) who want their privacy. You could try adding two - one with, one without a cover - and see whether that makes a difference.