A friend's company announced layoffs, they are going to be informed within the next month. My friend is in the first few months of her pregnancy, the employer is not aware of that yet as it is too early in the pregnancy.

Is she protected for a period of time because of the pregnancy? Does she have to inform them before they potentially fire her to be protected?

She should inform them ahead of the formal notification.
https://www.ch.ch/en/maternity-leave...96%20per%20day.

Yes do it before you get the notice, then she can't be fired at all until she's back from maternity.

Please don't confuse maternity payments benefit eligibility (which only commences after birth) and maternity protection, which can commence upon formal pregnancy diagnosis.

Additionally for all insurance-related purposes, there is a general obligation to inform of a potential later claim as soon as possible (in this case the employer).