Potential Maternity Leave Discrimination?

I’m writing this on behalf of my coworker because this seems fishy to me but I’m not entirely sure. She recently informed her supervisor that she would be taking a leave in June to have her baby, and received and email yesterday which says:

“In preparation for your upcoming leave, we’ve been reviewing the current schedule. To ensure seamless coverage for your shifts and provide valuable learning opportunities, we’re considering a change to your schedule.

Specifically, we’d like to transition you from your current night shift to either a Sunday - Tuesday or Sunday - Wednesday day shift. This change will help ensure adequate coverage while providing opportunities to engage in additional duties, increase interaction with other team members, and offer further learning and growth within the organization’s mission.

We anticipate this schedule change beginning in March 2025, with an official start date to be determined.”

She currently works 4 nights a week, so option 1 would effectively cut an entire day out of her schedule. And option 2 (swapping to days) would retain her hours BUT remove the night shift differential that she makes overnight. Is this legal? What would be the best way to proceed in either case? Thank you!!