Hello Jusy and thnak you for this question.
I'm sorry to hear about what's been going on.
As she is an older girl and this diarrhoea is continuing and not responding to symptomatic therapy, a vet visit is key, so we can determine what is going on and what therapy is needed.
If you want to avoid a trip to the clinic, you can request a home visit.
As she jas kidney disease, this may have progressed, so the toxin levels are causing the diarrhoea.
However, there are many other things that can cause diarrhoea in an older cat including an overactive thyroid, intestinal disease, liver disease etc.
A bland diet and probiotics are wise.
We also want to ensure she is not becoming dehydrated and can offer e.g. cat soup and rehydration solutions such as Oralade.
Do also ensure she is up to date with a broad acting wormer such as Fenbendazole.