Youch. Yuck. I would guess as well that she is telling the truth. However, her asking her brother to do it to her takes it to a new level.
set up the clock, but I'm not sure after a day with the clock at home if I'd be comfortable with this situation.
Good question-- bio dad?
I would guess she is not fibbing. But if you aren't sure and want to know what your husband is doing when you are gone, there are these secret-camera clocks that can be set up to film the home when you are away. If you think he won't notice, set one up. Is your husband her biological dad?