It was kind of a "perfect storm" situation.
We thought that the bedroom door was locked, but it's an old lock and it doesn't latch unless you put pressure on the door. We were having sex in the en suite bathroom, not in the bedroom. The bathroom door was open. We didn't hear our daughter come in. We didn't see her for a while, and she was basically like a deer in headlights. Even if she had spoken up, it's not like we could have covered up. But she definitely was way more than any of us would have liked.