Perhaps all you'd have to do is tell her that she's left you no choice but to call the police and file a stolen property report against her. Faced with that possibility, any semi-reasonable person would capitulate and turn over the property.
We have had a hard year with PTO with year already. Due to not following by-laws or prodecure and giving PTO a bad name due to behavior our president was asked to resign. Because of events last year she was also acting Treasurer last year. Our bylaws state that the file and papers need to be given to new officers by July 1st. They were not passed on. After her resignation we have given her a letter stating the items that need to be returned and by a certain date (last week). The principal and officers signed the letter.
Sadly...we have not gotten the requested items from her. Is there a way to get these from her? I hate to bring police in, but we need all the records.