Sorry for your loss. Mourning is something we all do at our own pace and time. Maybe you would like to make something to remember your sister by and get back to the other quilt stuff later. As for quilt projects we all start something and never seem to finish it. UFOs are a part of quilting. I volunteer with a group of ladies at our local Senior Center. We handquilt tops that have been donated by members or their families after they pass. They are then raffled off to benefit the programs at the center. We have a huge closet there full of fabrics and half finished projects that have been donated to the center. I will be sure to make a note to my daughter to donate my stuff when the time comes. I know that I will never live long enough to use up my stash.
The only way I get some things done is to kind of shut my mind and "just do it". There are many things in life like washing dishes or changing messy diapers that have to be done. That is the only way I can get through certain tasks or times in my life.