"Why do you want to know?" Might have been good response to memorize so you can deal better next time. it will give both of you time to reflect on it and come up with better questions and answers and or move away altogether so everyone can stay civil.
My mom didn't know that my dad was in Germany during WW2 until a few years ago. She knew he was in the service during the war because he'd mentioned something about being in England once. Dad passed away @ 15 years after he'd returned, and my mom didn't know that he was ever in Germany at all till her mother in law had died and some letters my dad had sent his mom from during the war came her way.
Same with my wife's father. 442nd and they raged across Europe. My wife knew her dad and Uncle were in the most decorated Army unit in WW2, but one day we're sitting watching TV and some show come on detailing i companies role in the rescue of the Lost Battalion. My wife heard "I" Company and her ears perked up because her dad had been an I company member, but she had no idea of the **** that entailed or that only 8 of the 200 I company members had survived that single engagement. Her dad had never said a word of it. I eventually learned lots and lots of stories by just asking some generic question like "what was the scariest thing you experienced" during an appropriate moment, and Kiichi opened up to me, maybe cause I'm a vet. Once I was conveying a few of these stories to my family after Kiichi had passed on from a heart attack, and my surprised wife had not heard any of it or anything like it. Nor had she thought to intrude and ask. I'm telling her, second hand, about her dad being shot dead center in the chest near Pisa in Italy. How his buddies and him opened up at the same time and the ensuing chaos. Her mouth is wide open in shock and surprise. How Kiichi remembers being on his back in the tall grass and seeing the sky when the medic leaned over him to help him out, how the medics head explodes from gunfire and then he collapses right on top of Kiichi. How he had to free himself from underneath (like at 110 lbs soaking wet) get out of the area and then walking 10 miles to the aid station because he wanted the buddies who were real hurt to have the few remaining trucks to get a ride to the distant aid station.
Not the kind of thing a man wants his daughter to know...or ever experience, even vicariously. Not the kind of thing she would ask.
I think in some ways it's society that has changed.