Hi Bryan
I don't know if my knowledge on the subject is upto date, but the explanation I give to my clients has been the same for the last 20 years or so. Here goes.
Soiling from either end of an animal, or human, have a chemical reaction on the carpet fibres. Normal cleaning does not counteract this chemical reaction. It can, however make the chemical reaction non-reversible, so it is important that the first action post accident is to absorb as much soil as possible, then treat with a chemical neutraliser.
As your client has already attempted to clean up the soiling, I suspect that she has created a non reversible chemical reaction which can only get worse rather than better.
As a footnote, I feel it is prudent for all CC's not to promote a stain removal service, but to merely say that they'll treat stains.
Safe and happy cleaning:)
Ken