There are objective factors around what happens exactly to the person that makes it more stressful. The introduction to your question seemed to be getting at why the same thing may happen to this one person who then develops PTSD, and the same thing happens to another woman who recovers fairly quickly or easily. Those are individual differences that do exist. We haven't been able to examine every single individual difference, but one of the things that has garnered the most interest, at least in the legal arena in the United States, has to do with previous victimization. We know that previous victimization makes one more vulnerable to developing anxiety and PTSD, even if the stressor is not as severe.
We know the rates of childhood sexual abuse in the United States are somewhere around 25%. If someone comes from a home where she may have experienced sexual or physical abuse as a child, or maybe she's partnered with someone who is abusive, all of that victimization can predispose her then to greater damage, even if it's not as severe as what her previous trauma was.