"A co-worker feels pressured to share when she's thinking about getting pregnant. No one has said it outright, but has mentioned in passing that they need to know how to back up her role if plans on taking time off. What are her rights here in California?"
Disclaimer: The following information was not prepared by an attorney and does not constitute legal advice. We are not providing legal counsel, and nothing said on Women.work is intended to be legal counsel. If you need legal assistance, conact an attorney or your local legal aid.
If your friend were pregnant, both the FMLA (Family Medical Leave Act) and the CFRA (California Family Rights Act) state that an employee should give 30 days advance notice before taking leave if they are able.
From the US Department of Labor: "To take FMLA leave, you must provide your employer with appropriate notice. If you know in advance that you will need FMLA leave (for example, if you are planning to have surgery or you are pregnant), you must give your employer at least 30 days advance notice. If you learn of your need for leave less than 30 days in advance, you must give your employer notice as soon as you can (generally either the day you learn of the need or the next work day)."
From the California Department of Fair Employment and Housing: "An employee shall provide at least verbal notice sufficient to make the employer aware the employee needs CFRA qualifying leave. The notice shall state the reason for the leave and its anticipated timing and duration. An employer may require 30 days advance notice before CFRA leave is to begin if the need for the leave is foreseeable. If 30 days is not feasible (e.g., not knowing when leave will be required to begin, a change in circumstances, or a medical emergency), notice must be give as soon as feasible."
The tl;dr version: If your colleague were pregnant, she doesn't need to give notice until 30 days leading up to the day they are taking leave. Before she is even pregnant it is none of their damn business.
Your employer making these comments can go as far as be considered harassment. From the Legal Aid Society - Employment Law Center: "Harassing or unwelcome conduct relating to pregnancy, childbirth, or related conditions is unlawful when the conduct creates a hostile, intimidating, or offensive work environment, or when it interferes with your performance at work. It is also illegal to harass a woman because she is perceived to be pregnant, even if she is not."
Even if she is not.
Tell your friend to go to HR and make a complaint about these comments. Family planning is an intensely private topic and can be a difficult time in a woman's life if there are complications and or health issues. Having to worry about colleagues commenting or pressuring her on top of all of those concerns is not only bad for the workplace but the stress could also be bad for her health.