As do most plumbers, although garbage disposals generate a lot of business for them in the form of expensive call-outs, snaking of clogged lines, etc.
That’s one that I knew, but didn’t really know until one of my roomates demonstrated that he didn’t know that at all. That was a mess that ended up having to cut out a section of my basement wall to be able to cut out the clogged pipes, as an auger just wasn’t making any headway on it.
(ETA: uncooked rice, too, should never go down the drain.)
I read it as that the OP’s mother is trying to use the “environmentally friendly” card to put food waste in the sink disposal (where it won’t stink up the house), rather than in the garbage.
Actually, it was more that I played the environmental card. She thinks that it’s environmentally neutral.