Despite 'clearly' reading the entire article and having it pointed out, you missed/ignored the second part.

"Her team was reassigned" (during her extended absence) - reasonable. Disappointing, for her, perhaps, but reasonable.

"and she was placed on a PIP" - she comes back from maternity and is told, formally, 'your performance is unacceptable and is going to have to improve to stay at the company'. This just screams vindictiveness. "Your pregnancy inconvenienced the company / team, so here's a formal black mark for you, often used as an excuse to be able to fire you at any time in the future".