Partner's Boss Keeps Asking Coworkers If She Is Pregnant

Hey, y'all. We're in Texas, and this feels discriminatory, but I'm not sure that "potentially being pregnant" is a protected class, or if this is grounds for consideration of a hostile work environment, or what.

When my partner was hired at a doctor's office, she was asked if she had any kids or planned on having any kids during the interview (which is, as I understand it, a big no-no because it can lead to gender discrimination). At the time, though, the answer was no; I had a young child from a previous relationship, but she herself had no children, and while she wanted to have some eventually, it wasn't on the radar as something feasible at that stage of our relationship. The money was well over standard for the industry and job title, so she accepted the position.

In the five years since then, several other people at the office have had kids, and the doctor is now very concerned about my partner (who is an integral part of the practice and the oldest "childless" employee) taking leave or quitting if/when she gets pregnant, because the business cannot function without my partner under it's current structure (to the point that she can only take PTO when the office is closed, which... sort of defeats the point of PTO, but I digress).

The doctor always phrases the question as affirming the negative, i.e. "You aren't pregnant, are you?", which is pretty indicative of how negatively she views pregnancy. My partner has continued to respond that no, she isn't, but the doctor doesn't believe her, and has recently started asking all the other employees if my partner is pregnant.

This in and of itself is, in my opinion, morally wrong; it shouldn't be the doctor's business whatsoever until someone puts in an FMLA request or modifies their availability. But to make matters worse, we have been struggling with infertility (me, not her), and it has been really hard on her mental health... Getting bombarded with these questions every day is not helping.

I'm wondering if there is an avenue to pursue legal action against the doctor for creating a hostile work environment, since she isn't exactly being discriminated against for being pregnant, she is being harassed because she might eventually become pregnant and her employer doesn't believe that she isn't pregnant. Is harassment for an assumed pregnancy enforceable if she isn't actually pregnant? Texas is very employer-friendly and Google is failing me. Thank you in advance!

ETA: Business has a single-digit number of employees, not including the doctor.