My question: is this a tactic to keep me from talking about something that she perceives as damaging to her?
I have had this problem with my husband for years. I have tried to talk to him about it. The best response I have gotten is something along the lines of, "I am not trying to interrupt you as much as I want to get out what I want to say before I forget about it." Basically, he isn't really listening to me to listen. He listens to me to respond. While I am talking, he is thinking about what he wants to say. The minute he gets a thought in his head, he blurts it out and interrupts me.
This has slowed way down and gotten a lot better. I think I may have gotten through to him a bit when I would stop talking when he would do that to me. If he would ask what I was going to say, I would disengage and end the conversation. There for a while, I just let him talk and didn't really say anything other than a brief acknowledgement that I heard him. I might validate or ask for more information but I did not share anything. I stopped trying to have a two way conversation with him there for a while. I stepped off the roller coaster.