That must be very triggering!
I can't think of a sentence that would always be appropriate. It depends on the situation.
Giving short answers like "yes," "no," or "I don't know" can discourage a person from prying further, especially if it's coupled with a clear attempt to change the subject.
Other ideas for when that doesn't work: you could suddenly "remember" an appointment that you're late for if it happens during the day. In the evening, you could supposedly get a text from friends or family saying that they need a sitter or something. You could tell them that you're expecting your husband to arrive at any moment if they don't know you at all. When I was younger, this is what I would do to get out of conversations with people who were making me uncomfortable.
In person, I'm not very assertive either. I usually try to avoid confrontation whenever possible because it doesn't feel safe. I have CPTSD, autism, and ADHD too.