Is it fair to my PhD student if I ask them to do "miscellaneous" work for a paper they're not going to be a coauthor of?
Preparing a graph from already-generated data, to me, doesn't merit co-authorship but would justify a mention in the Acknowledgements. However, something that takes two days out of a student's time (even if it would only take you 3-4 hours) seems like a lot to ask for just an acknowledgement. 

How useful is learning the process? If it's legitimately training that's important to her future career, that might tip the balance toward asking her to do it. However, I think my default would be to do it myself.

One other part of the equation (probably and hopefully only a very small part) is that the student is female, based on the pronouns in the question, and female scientists are often expected (from unexamined assumptions) to disproportionately look after administrative work.