This is such a refreshing take on a complex and extremely frustrating issue. I think you really nail some important motivations that need to be addressed (namely the all too frequent dismissal of women and their pain by doctors, the isolation inherent to motherhood, and the idea that these conspiracies give meaning or purpose). I would also add control as a variable. With all the systemic pressures stacked against women (lack of paid childcare, housing affordability, income inequality, healthcare, etc.) conspiracy theories and the ability to exercise control over personal decisions about health is really attractive to people who otherwise feel powerless over their lives. This also explains the otherwise odd overlap of anti vaxx with gluten free, paleo and other lifestyles that at their core offer a sense of control. Most of these women feel helpless when it comes to addressing the big structural underlying forces at play, but they can exercise control over what they eat, etc.
I think it’s also important to point out that this is only a tribal issue for the most extreme. I’ve written before about the need to put a cost on conspiracy theories. Proposals to provide $1500 as a stimulus bonus to those who get vaccinated would really separate those who are never going to be swayed from those who find it easy to share something on Facebook, but won’t actually put their money where their mouth is. We’ve seen this with vaccine requirements in CA where some have chosen to homeschool or move out of state, but the vast majority of people complied when it became too much work to rearrange their lives around an issue that wasn’t as deeply held as might have first appeared.