Could be what Colin or what Mark have pointed out.
Get back to her and tell her to give it a couple of days for the odour to disapear (should really disapear within 48 hours) explain to her its highly likely the backing of the carpet that is causing the smell. Point out that its a common problem with BW (minor bullpoo) and that you apologies for not qualifying her before you started.
Its happend to me twice before, customer rings says it smells acidic/p-like and then call me back to say its gone! happy days
In the future try chemspecs urine contamination treatment on the puke. Its designed for pish but does a great job on many body fluids.
Also, try nemsis odour nuetrilisor. Its a bit expensive but does a great job!!