She was talking about her characters: onions, mushrooms and nuts. Before you think I've lost my marbles and begun a cooking blog, let me explain her meaning.
Onions are characters, like her Jamie and Claire, that keep revealing themselves, layer by layer as she goes further into the story. She learned more about them the more she wrote their characters. Like peeling an onion.
Mushrooms are characters that just show up. They are sort of a surprise at first. She said her Lord Jim character just showed up on her page. They seem to grow out of nowhere, but become an important part of the story.
Nuts are her characters that she is stuck with, or has to use because of history, the genre, or the story itself. She talked about historical characters, such as Charles Stuart, as well as characters the story created, like Jamie and Claire's daughter. Those characters she said she had to just "live inside" to understand them and fit them into the overall story.
I'd never thought about my characters this way. What about you? Can you classify your characters into Onions, Mushrooms and Nuts?