now oculus is no more a developping company but a delivering (? at least it should !) company, most of the people will jump out of the ship. Now day to day problems will be about pushing box at fast rate and giving support, that's usually not what people working in a startup are looking for.
That doesn't mean anything. Brilliant people get bored quickly. She probably helped solve the big challenges in front of her getting the Rift to CV1 and decided to do something new. From this point out the Rift development will probably be more iterative than revolutionary (at least for a few years). That might not be as interesting to some people who are really looking for a challenge.