I can't believe she is using yahoo email for sensitive items. Being that she was locked out odds are someone just went in and said they forgot the password and then were able to answer the security questions accurately. If you can answer two of them it lets you reset the password, thus she was locked out.
Sarah Palin's yahoo email was hacked this way, they clicked on I forgot my password, correctly answered what highschool she went to and when she met her husband. Always answer those questions with made up answers you can remember. Never know when your life will become public and questions like that can be answered by the general public.