I understand the seriousness of this situation, but perhaps a comedic outlook might be in order.

In my opinion, there is actually a lot of untapped comedy in the very idea of a well kept house. And dinner on the table for a husband coming home? Now there's a real joke. And a kid expecting to sit on the stairs not allowing me past might enjoy the image of the results of a weak bladder. At least the other kids would probably enjoy that image.
And when she accuses you of being the bad stepmother, just hand her a broom and call her cinderella. Some of her whines and accusations are probably becoming repetitive and you can anticipate them in a monotone voice as if from a tape recorder when you see them coming. My kids hate that, but I love it.

I know ricicule can be hurtful, but if you look at the situation as a scene in the human comedy it really can be funny. Laughing with my kids at their imperfections and mine has diffused a lot of potentially serious situations. Tragicomedy is a wonderful way of looking at things. And it can actually be therapeutid for the whole family to realize that they are loved despite their ridiculous habits, whines, dramas, and general all around silliness.

I was reminded of that at lunch with my youngest. Here she is a CPA out of college with kids of her own and she's still whining about some halloween in Jr. High when I forgot her at school. If I say anything even remotely critical. She goes into this melodrama about how I warped her for life by forgetting forgot her at Halloween. And when she complains about something I have done I say she should be thankful I didn't leave her at school on Halloween. And any problem she has with her kids we bring into focus by just saying "Halloween." Then we all giggle and move on. Maybe you can find something like that to smooth out the rough spots.

A little comedy can ease a lot of bad feelings.
smile