Re: Am I being too hard??
My sister was always one for losing stuff -- she once lost a winter coat in the dead of winter when it was freezing cold. Mittens, hats, clothes, shoes.... Library books and videos were the worst. Got to the point where my parents FORBID her from checking out books from the library. She was just one of those kids that just couldn't keep track of stuff and her mind was always elsewhere.
I'd give her the benefit of the doubt this time and if it happens again or she starts making a habit of losing things and blaming others, then your husband may need to have talk with her about it. If she was dishonest about it, then she'll more than likely do it again.