Elder Anemic Cat with Renal Disease just started eating litter. How do I get her to stop?

As the title says. My cat is elderly, probably 15 years old, idk her true age. She last month got tested and was found to have anemia and kidney disease, stage 3 or so. For a while she had a lack of appetite which was very unlike her and then after starting her medicine it went away and she is on special kidney friendly prescription food now too.

HOWEVER, ever since starting her anemia medicine, I started noticing cat litter around her lips and mouth randomly through the day, and just now I discovered her in the act eating her litter. I know anemic cats will eat clay litter for minerals and iron, but her litter is crystals, and also she only started this after starting her anemia medicine which is suppose to be helping her... On top of that, before starting her anemia medicine she got a booster of iron and B12(I think?).

Is this a sign the medicine might not be working? Idk what to do or how to get her to stop.