Hi Helena,
Sorry for the delay in replying
I hope Storm is doing OK. I cn't really offer much advice other than the fact that she has a litter tray indoors, in the warm might be the reason she is using it more

As for the smelly poos cat poop naturally smells pungent due to a carnivore diet high in protein, which produces sulfur compounds and nitrogenous waste.
While a mild, consistent odor is normal, extremely foul-smelling, lingering odors may indicate digestive issues, parasites, or poor-quality food. Managing this involves high-quality diet, daily litter cleaning, and veterinary checks.
You mentioned she was a hunter so it could be parasites.
It might be worth a vet visit just to rule out the obvious issues.