It sounds like this is a very big issue for you. It is a deep rooted pain.
My T would first have you make certain your resources for support are in place before you head into working on the trauma pain of your sister's death.

Make sure you know what you will do when the sorrow is too much.
Have people in place that you can call or email in the middle of the night.
Be sure you are taking care of yourself and get plenty of rest durring that time.
The way T explained it was like preparing for open heart surgery.
You don't want to go into something this serious when you have a planned marathon the next day.

Sometimes we have to face trauma work and we don't get the chance to plan how we will work with it. But there are times in therapy when we do get to plan those big issues out in advance. You know how you will respond to the emotions this will bring up for you. My T said that when he was doing his own planned EMDR around his trauma issues that he knew it would throw him under the bus, so he took off work and set aside a couple of weeks just for him to work through what he knew it would bring up for him.

Bottom line is to do what my T said his T tells him to do for trauma work "Be percise."