The boycott happens in Chapter 19.  The students discover a maggot in the grits.  Anne visits the kitchen to investigate and discovers that there is water leaking into the supplies in the pantry, creating a breeding ground for maggots.  First, she decides to visit the house of the president, but then realizes he is out of town. At that point she says,

We don't eat until he gets rid of Miss Harris and that leak is fixed! (209)

Of course, the students could not eat if they were going to boycott the cafeteria, so Anne used her own money for food supplies, borrowed some hot plates, and the students cooked for themselves.  Although she did not manage to get rid of the horrible Miss Harris, the leak was fixed and the spoiled grits were thrown away.