Her mom and some other characters refer to Donkey as a "mathematical genius", but I see no evidence of that. Rather, I would describe her as a math nerd, someone who likes math.

Among the things she likes most about math is the certainty of mathematical truth. She begins keeping a notebook of true things, including not only facts from "Garden of Logic" but other sorts of "truths" as well, after which she writes "Q.E.D", an expression she learned from Schweiss' book. For instance, talking about her mother and her ex-boyfriend in her notebook she writes "Rose Thorn Loves Titus + Titus Loves Rose Thorn → They should get married, QED."

Most of the time a whole number is mentioned, Donkey factors it (sometimes but not always into primes). She is interested in perfect numbers and describes chopping a snake in half as "bisecting" it. She appreciates the palindromic nature of Pascal's triangle, as long as one only considers a finite piece of it as a time.

Although she seems to like most mathematical ideas, Donkey really hates the concept of infinity, which she associates with death. She likes the number π, until she learns that its decimal expansion is necessarily infinitely long. As noted above, she likes prime numbers, but says "ugh!" when the book shows a proof that there are infinitely many of them. Her hatred of the infinite keeps her from learning any calculus.

Donkey tells her mom that she wants to learn topology because Professor Schweiss is a topologist. However, she is surprised (and has a surprisingly sexist reaction IMHO) to the discovery that Schweiss is a woman:

Towards the end of the book, a change in her family structure as well as this new information about Schweiss has her reconsidering infinity, and she mentions the possibility that she will learn calculus after all. (And, I should mention, that the epilogue of The Waters is labeled "Chapter ∞".)