Kay, I just snorted my green tea through my nose at the computer screen. Nope, you're right and your mother in law is NOT. My poor washing machine does NOT smell like poop even a tiny bit, and it was used for almost three years solid, day in and day out, of diaper washing. Breastmilk poop basically dissolves into the water and rinses away. When they get to real food poop, you have a few options. You can dump it first into the potty, use a liner that flushes and dump that into the potty, or use a fleece liner and it'll dump easier into the potty (if it's sticky for some reason). Basically, I NEVER had an issue with washing poopy diapers. I think she's just afraid of cd'ing, because of what they were like when she was diapering. THey are SOOOOO different now...even were you to use basic prefolds, the covers ROCK, so you don't need pins. Anyway, that's my 0.02 about the poop in the machine.
I don't use AIO's because, with a snug fitting cover, and/or fitteds with elastic at the legs, I can often get three or four uses out of a cover before I have to wash it, as opposed to having to wash the whole shebang every time with an AIO. Just a thought. I'm sure there are PLENTY of people here who can give you advice about their favorite type of AIO or pocket, though.