Does the personal representative of an estate have a duty to notify the beneficiaries of any ongoing estate proceedings? 

I am sorry for your loss. It appears that your sister has filed a petition - request - with the court to recover assets that she believes are part of your Father's estate that are no longer present an accounted for.  The Personal Representative of an estate has a great deal of power to gather assets that they believe are part of a decedent's estate. It is my understanding that there has to be "good cause shown" - good reason to believe it is true - that the asset has been in some way "dissipated" - taken - from the inventory of the decedent by someone who had no right to do so.   

As a beneficiary you have the right to inquire as to what is going on.  If you feel that your sister is not being forthcoming with information then you can go down and review the file yourself in Court.  If it is really difficult obtaining the status of the matter thereafter most states allow you to file certain requests for information - accounting, etc.