Of course, the writing is beautiful. Mathematics is not the central focus of the story, but neither is it avoided (as in the film) nor is it presented inaccurately. An appearance by Poincare discussing his prize, many mentions of Weierstrass (her thesis advisor), and technical terms such as `theta functions' or `partial differential equations' are used well in this character study of a woman living at a time when her skills and interests were not fully appreciated by the rest of society:

An author's note explains that Munro ran across an entry on "Kovalevsky" while searching for something else in the encyclopedia and became enthralled. She suggests that "Little Sparrow: A Portrait of Sophia Kovalevsky" was a primary source. I am assuming, therefore, that it is historically accurate and well researched (at least as historical fiction goes). However, I am not sufficiently expert to be able to say this definitively. In any case, it is certainly believable.

In addition to appearing in the collection, this story was also published in Harper's Magazine (August 2009).

Update: In 2013, Alice Munro was awarded the Nobel Prize in Literature for her short stories. This story in particular does not seem to be cited as being among those that resulted in her selection for the prize, but I do find that many of the news stories announcing it were themselves entitled "Too Much Happiness".