I am so sorry for your loss. My mother died over 20 years ago and I still miss her everyday. I believe that you are fortunate to get them back. I think storing them for a while is good advice. Later, even though it will still be difficult, I think you will be grateful to have them and to know that she loved and cared for them as you would. She may have even told your sister to give them to you. Time really does heal and I imagine she would want you to have them.