My wife (also a tech exec) could've done this too (though she'd taken 4 weeks off, with an experienced full time nanny). Some women are just super organized. And yes, some women are less sensitive/susceptible to hormonal fluctuations. We have 3 children. Each has quite different personalities, all of them fairly attached to their mom. If you got lucky, things are pretty smooth :) You can solve the breast feeding problem by smart combination of pumping and feeding. All my kids were on breast milk longer (> 1y) than average (drop to 43% at 6m). I got to spend more time (still less than her) with my kids too, changing diapers and picking up/dropping off to/fro school etc.

Based on what I've seen how Marissa operates (organized and data driven), I'd say she'll have no problem (on her side) to handle her first pregnancy and child.

As an XY! Good luck Marissa!