McKellar studied at the University of California, Los Angeles where she earned a Bachelor of Science (B. S. ) degree summa cum laude in Mathematics in 1998. As an undergraduate, she coauthored a scientific paper with Professor Lincoln Chayes and fellow student Brandy Winn titled "Percolation and Gibbs states multiplicity for ferromagnetic Ashkin–Teller models on Z2{\displaystyle \mathbb {Z} ^{2}}. " Their results are termed the "Chayes–McKellar–Winn theorem". Later, when Chayes was asked to comment about the mathematical abilities of his student coauthors, he was quoted in The New York Times, "I thought that the two were really, really first-rate. " For her past collaborative work on research papers, McKellar is currently assigned the Erdős number four, and her Erdős–Bacon number is six.