That employee needs to get over her simping mentality and sue for the gender discrimination Bungie is blatantly guilty of. I don't give a shit if they happened to be doing a mass layoff at the same time; you don't get rid of somebody right before their already-scheduled maternity leave!
I'm not sure you have a case if the percentage of women on maternity leave in the fired group is roughly the same as in the non-fired group.
If it isn't illegal to fire people taking maternity leave specifically, which I don't think it is in the US, you're out of luck. The only illegal thing is firing people because of maternity leave. Since there was a mass layoff, it can easily be argued that the maternity leave was not the reason.
The US needs better labor laws, and thus unions. An individual can't do anything against it.
The decision to lay the person off was made before the maternity leave was scheduled, in which case I'd argue she has a case for detrimental reliance, or
The decision to lay the person off was made after the maternity leave was scheduled, in which case a prima facie assumption is fair to make that the taking of leave obviously colored the supervisor's evaluation and contributed to the layoff, and the burden is on the employer to prove otherwise.
In fact, there's an argument to be made that they must terminate her, because Terminating everybody but those with scheduled maternity leave has a disparate impact on employees who are not pregnant.