The key is that you need to align incentives for employees, investors, etc by demonstrating a long-term commitment to the company. Lots of more nuanced discussions of this topic exist but here's one I have at hand: http://startupclass.samaltman.com/courses/lec18/

They likely were giving her additional grants later in the life of the company upon reaching certain milestones to make up for her dilution at a strike price that required millions of dollars to exercise. You can get away with founder stock very early on, but at some point, it becomes untenable as the value of the company grows.