Apart from the fact that she didn't want to talk about it! I had been trying to explain how a female partner who I had when DD was born, but separated from when DD was three, isn't part of our family any more. DD still spends time with this ex regularly, but I am almost non contact with her. It came up in conversation while we were getting in the car to go out. She went quiet and I asked her if she was confused about who her family was, and she said "I don't want to talk about it". Then I asked her another question along similar lines, and she repeated it.
I feel so bad about this mess I've put my daughter through. I wanted to keep the communication open about things with her, at age-appropriate levels, hence my attempt at discussion.
I did keep talking, and she said that she thought I'd done the wrong thing because I'd left ex when we were married. She attends religious school and I think this may have come up as part of the ten commandments.