...but she was wearing that when she was watching the movie with her brother? Where was the shirt located at in the home? They better not be messing with it until the proper forensic folks get their gloves on it. The shirt could tell a story, or it might be nothing but dang...I hope they're not messing with it.
7 yo's are perfectly capable of dressing themselves, so she probably got dressed after mom saw her last.
If she is like my 7 yo, the shirt could have been tossed anywhere - hamper, closet, under the bed, bathroom...