If you're an executive at Facebook, you should know how to research negotiation and compensation, and figure out a living situation where you're saving money. You're in the big leagues. If Sheryl expected her to be able to hire a full time nanny, then that's an excellent time to renegotiate a salary than can afford that.
If you're an entry-level worker who can't make ends meet in San Fran then of course I sympathize greatly! But if you're an executive at Facebook making enough money that you can even consider a full time nanny... you're not facing any level of "hardship" by which an offer of even more money in exchange for non-disparagement could be considered "coercion". Nobody is in poverty here. Nobody is going to wind up hungry or on the street.
So yes, she was 1-3 months away of poverty while caring for a baby.
Poverty can come really quickly, you just need a few incidents to stack.
If I made, say, $300K/yr and was living paycheck-to-paycheck with zero savings after many years with the company, I'd say I was making highly irresponsible spending choices.
And she had a husband too, who sounds like he was working.
So something's just not adding up. It doesn't make any sense that a director-level executive at Facebook is 1-3 months away from "poverty".
As that became more important her role grew but she was never really promoted.
She also was not well informed about how tech compensation works and negotiated poorly (no stock) she came from an NGO background in New Zealand.
Her salary was probably quite a bit more than the average American but she was living in expensive areas (DC and SV) and interacting with extremely wealthy people. At one point Sheryl Sandburg got annoyed that she was leaving work for childcare and told her to hire a live-in nanny. She was living paycheck-to-paycheck on a high income with no wealth accumulation (many such cases).