I'm stumped
"Sorry Ma'am, dog shit happens." Like you said.. it's not your fault her dog messed up all your hard work.
You don't give a "If your dog craps on your floor, you throw a wild kegger and , beer, wine, and crab dip gets spilled all over the carpet in the next 4 weeks, I'll be back to clean it pro bono guarantee" do you?
If she brought her car to the repair shop to have her fuel injection system fixed to the tune of $400. but 3 weeks later driving through town her dog hits her shifter and throws the car into reverse and she blows her transmission... does she expect the repair man to fix her transmission for free for the same reason she thinks you should clean her carpet for free?!! That's asinine!!!!
Do they have any idea how much we'd have to charge to cover losses for making free return trips for completely separate cleaning issues? That REALLY is taking advantage of your generosity.
I'm sorry, yeah it sucks being her, but c'mon... you know what.. she's probably not going to call you back again even if you do clean it for free because her opinion of you has changed in her mind.
I had a similar situation happen, I gave a slight break because I was in the area and it wasn't nearly as severe an issue as you have but I didn't away my services either.
Good luck dude,