Where did she get it from? (or from whom? - she should be able to say.) In what condition was the laptop found, on her desk? opened? screen saver on? or powered down? in a pile, covered in dust? any fingerprints or other signs of use? Any removable media present? They can look in her office for passwords written down. They can check her mobile devices for password managers and compel her to unlock those.
Understand for the case to even proceed to indictment (which happened last year), they have done all of this work to make sure that their case is pretty solid. There are pretrial hearings, and depositions and other things which lawyers do to answer all these questions about whether they can prove that she really should be able to provide the password.