To get further cooperation from your sister's girlfriend to pack up your sister's belongings, you should get a written, signed and notarized power of attorney from your sister authorizing you to do as what she supposedly told you to do. When received, provide a copy of this document to your sister's roommate.If the house is a rental, provide a copy of this power of attorney to the landlord and see if he or she will allow you access to the house to pack up your sister's belongings.If you still receive no cooperation from the roommate and the landlord, you should consult with an attorney to assist you in getting access to the home. Perhaps a letter from the attorney mentioning the power of attorney to the roommate and landlord will get the desired access for you to do what needs to be accomplished.Good luck.