Discipline Dilemma: When BioMom Disagrees

It was a morning like any other.
Cinderella was eating breakfast getting ready for school. I was in the living room nursing The Mouse.
When She got up from the table to put her bowl in the dishwasher I tell Her the dishes are "clean" and to put her bowl in the sink.
Oh, ok.
She goes back to the table out of view. I hear the sound of her spoon scraping along the bowl. When she steps back into view her cheeks are full like that of a chipmunk who is busy foraging for nuts before a long winter's nap.
What's in your mouth?
Cheerios. Her words are muffled by the soggy cereal in her cheeks.
What were you going to do in the dishwasher?
Put my bowl in it.
With the Cheerios in it?
She gives me a sheepish "yeah."
I ask why as I struggle to keep my head from exploding.
Because I was full.
My thoughts then turn to the night before when I ran the dishwasher and had to stop it during the final rinse cycle because it started making a horrendous screeching sound. A noise that sounded like a cross between a rusty helicopter rotor and fingernails on a chalkboard. It occurs to me that the mystery of what's causing the sound might be unfolding before my disbelieving eyes.
I then think back to the prior week when I found not one but two bowls with soggy Cheerios in the kitchen sink over the course of two days. Each time Cinderella turned out to be the culprit. Both times She was asked not to waste food and to please.don't.pour.your.cereal.in.the.sink.
How many bowls of Cheerios have you put in the dishwasher before.
None.
I ask again. And then one more time for good measure.
Each time She assures me that she is not lying but telling me the Truth. She has not put a bowl of Cheerios in the dishwasher before.
I give her the benefit of the doubt because what else could I do. I had not yet had my coffee so I did not think it wise to pursue this matter any further for fear of some under-caffeinated psychotic episode.
Later that evening after dinner She finally confesses.
What was put in the dishwasher to break it.
Cheerios.
So you lied to me this morning.
Yes.
I tell her to not say another word and please sit quietly on the couch while I pick up the tiny pieces of my skull and gray-matter from the floors and walls. We then both sit in the livingroom in silence as we wait for Hubby to get home to deal with this. These days I find myself deferring to Him more and more where Cinderella is concerned.

The dishwasher is brand new. Mr. Landlord installed it within the last year after our stone age one sprung a leak. It's one of those space-saver ones which means it.was.not.cheap. I recall Mr. Landlord bitching about how much this thing cost him.
Lucky for us, he works in the Product Repair department for a major home merchandise retailer and is bound to have access to whatever part has been broken.
Even luckier is that Hubby is very mechanically inclined and can fix anything better than McGyver so Mr. Landlord does not have to be troubled.
Unlucky for us, we are too afraid to call Mr. Landlord as we are two months behind on our rent.
After three days Hubby gives in and leaves a message. That was three days ago.

I am beginning to get dishpan hands. I would make Cinderella do the dishes but she barely knows how to wash herself (what is it with kids and soap, anyway?) so I am not inclined to entrust her with our family's dishes.

Cinderella is entering pre-teendom. The hormone fluctuations are apparent, the sneakiness and deceitfulness starting to occur with greater frequency. Punishment was handed down for this infraction (no TV for lying to me, no dessert for wasting food) but BioMom did not agree with it resulting in a 5 day stay of execution which results in a loss of effectiveness especially for a child that is borderline if not full blown ADD not to mention painting BioMom as the "fun" parent.
We realize that we cannot control what goes on in BioMom's House.
The discipline styles in each of our Homes are polar opposites. Hubby is concerned that this may compound the problem with Cinderella's behavior and cause her to begin to think of our Home as a POW camp.
We need to find a Happy Medium he tells me.

::deep breath::

Is there a Happy Medium with regards to disciplining a stepchild? One that will not create a double-standard and then resentment and rebellion with the younger BioChildren?