JMO but the way the Sheriff talked about the items found, I got the impression that her books were not inside the bag but were found at the same location. If they were inside the bag, I think she would have said so.
They confirmed her clothes were, why not mention the books as well?
If the books were at the same location, but not in the bag, then the particular arrangement should indicate to LE whether they were thrown or placed. But LE says they don't know if they were thrown or not. Does that imply the books were in the bag?