Did you at least get paid for the sofa, what is the excuse in not paying for that. I would definitely ask to see the carpet and a receipt off the company who cleaned it, if no receipt then their number so you can ring them. If she disagrees to letting you see the stains then contact the homeowner, if you are dealing with her then she should pay, if she says its the homeowner not willing to pay then she can't argue with you speaking with them. It just wouldn't be acceptable in my world, they wouldn't get away with it, i'd be at the door on a Sunday morning.
If she is scamming you then she will lose a cleaning customer.