If you've got anywhere local that sells home brewing stuff they should sell sodium metabisulphite... but I'd take a guess if you haven't got any, you're not experienced with it and would definitely NOT advise to go straight to a "real" job with no experience... these things need a lot of practice first!!
Hydrogen peroxide would probably do the trick as well but the same caution as above applies
I presume the urgency is because the coffee has only just been spilled? If it's been there ages and she wants it done at the drop of a hat I'd be much less accommodating tbh!
If it's fresh you might get a long way to fixing it simply by flushing it through with cold water and a liberal application of browning prescription.