When it said at the beginning of this story that "Katie’s father...is a physical manifestation of Order and Chaos," I presumed at first it meant that metaphorically. In fact, it means that Katie's father has the power to do things like arrange for the license plates of cars driving past her to convey the message that he has been trying unsuccessfully to contact her via text messages.
Her father challenges Katie with difficult and seemingly abstract questions about probability:
(quoted from Probabilitea)
His problem sets are always these abstract puzzles where she has to manipulate one probability distribution function to another using only an arbitrary—and, in her opinion, unfair and generally unhelpful—set of mathematical transformations.

But now, as he steers her towards working with her friend Jackson (who happens to be a physical manifestation of Life and Death) to thwart the plans of a gang of white supremacists, she finally understands why:
(quoted from Probabilitea)
Katie finally understands these endless problem sets she’s been solving for years. Her father has been drilling her for as long as she can remember on the various ways to manipulate order and chaos, always with the stern warning never to manipulate the real world in any way that materially affects anyone. He has also given her ever more ridiculously difficult math problems to solve. Put the two together and Katie can manipulate one set of realworld conditions into another. Not that her father has ever mentioned this to her. In particular, the solution to the first problem he asked her to solve by tomorrow sets up the conditions Jackson has asked for. Not only can Katie do what Jackson wants, she actually knows exactly how to do it. Well, at least in theory. If she’s solved that problem right.

Thanks to Gregory Cherlin who suggested I add this story to my database. It was published online in UNCANNY MAGAZINE ISSUE TWENTYEIGHT. 