In a nutshell, this feat is accomplished by:
1. Stay on top of the schedule through careful project management, collecting metrics to have realistic data on how long each task requires, and frequently revisiting and adjusting the timeline of the project.
2. Be flexible about the workflow, examining the way you have always done things and adjusting as needed to better work with a massive collection.
3. Think of it as data management. Use tools to repurpose data from one step of the project to another, and to analyze and transform the data once the box inventories are complete.
4. Spend extra time writing descriptions about each part of the collection to provide the researcher with important keywords to search for and context to understand the significance of the section. But do not spend time on description that is not aiding in searching, such as lists of document types in the collection inventory. Time should be spent on value-added description.
The slides and text for her presentation are available here