If they only pay lip service to the letter of the law and you return to find your job effectively gone, then that's still crap treatment that will disproportionately affect one gender, given the usual length of maternity leave compared to paternity
The other things could and should have been improved by Amazon. Their obligation is to get you back into a situation as close as practicable to the one you left.
what about the new manager? why should they have to change teams? basically what you're saying is that everyone on the team should suffer significantly so that one person can return to lead the same team with different members rather than just leading a new team that needs a manager?
If it's a massive career-impacting hassle for employees of people on leave at Amazon, where they "suffer significantly" that's yet more evidence for Amazon being a terrible place to work.
"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".
No manager with any sense at all is ever going to write an email like that, don't be ludicrous.