Otherwise known as Pressia and Partridge's mother, Aribelle is characterized more when she is absent during the book, instead of when she's present. When she is present in the book, she acts just as we suspected: kind, gentle, loving, and intelligent.
Then her face gets blown to pieces, so that's all we really get from her. Bye, mom.
But when she isn't present (which is most of the book), we can actually feel her effect on the characters. Ellery Willux tells Partridge in the second chapter, "Your mother has always been problematic," so even the evil dude can't seem to conquer her influence (2.73). Plus, "has always been" is not in the past tense… which gives us the first hint that she's alive the whole time.
But let's focus on the whole Swan Wife Story. When she tells Partridge this story, he's just a wee little lad. He just thinks it's a fairy tale, and that's about it. But Aribelle tells him the story as a code for him to figure out when he is older. Like, a lot older.
And guess what, it kind of works. Aribelle, even though she's either dead or absent for most of the book, is definitely one of the strongest characters. Not only does she plant a hidden message in her son's brain when he is younger, but she even martyrs herself to save the people outside of the Dome. Without Aribelle, there is no impending rebellion on the inside of the Dome.