Please help, not using litter box!

I'm sure this topic has been tossed around many times before but I really need help as I have a 12 year old female who has one foot back in the shelter.

I have had Jane and her brother Tarzan for about 2 1/2 years starting as fosters for almost a year. During the foster period Jane was a perfect little angel with no litter box issues but after we signed the papers she's turned into a giant pain in the butt. I am almost to the point of taking her back to the shelter because she has progressed from not pooping in the litter box, to not doing anything in it. I refuse to have my house smell like cat urine!

She has been tested for URI, kidney issues, and diabetes and all her tests are fine. She is generally a neurotic cat and also enjoys licking her stomach until it's raw and bleeding.

I don't know what else to try with her, we've tried Bach's remedies to calm her and make her less crazy but it's been unsuccessful. What else can we do to encourage her to use the box? I can't take much more of this!!

Given that she's up in years, it could be things like 1) her eyesight is going and she has trouble finding the box 2) she needs more boxes available because she has trouble holding it till she gets to the box, etc.

Leave more boxes around, in other words. My guess is it's age related more than behavioral, and we're all gonna get old - I wouldn't want to get tossed out for that.

I know there are people on the board who've successfully used cat diapers to solve litter issues.

I'd do a full vet exam, blood panel, etc. Is she declawed?

Is the litterbox big enough for her?
Is the litter right for her?
Any stressful changes in her life or yours?
Tried Feliway?
Tried "drugging" your kitty?
Do you have enough litterboxes?
Where are they located?
Is she getting picked on by other kitties when using the LB?

My foster was declawed, then re-declawed due to her claws growing back. She doesn't use the LB very reliably. Try Cat Attract litter or the litter additive. There are prescription meds "drugs" that help with going outside the box, but they're a last last resort.

I'd suggest Cat Attract litter (I think Dr. Elsey also has a senior cat formula now) and Feliway diffusers, and more boxes. I'm sure you keep the boxes scrupously clean, but we only have human noses. What has your vet suggested (mine told me about Cat Attract and suggested Feliway).

Also, make sure you've cleaned any 'accident areas' with an enzyme cleaner - and then clean again and again. Yes, a pain, but it really helped in my case.