Paddy -
I hear your screams and offer virtual hugs for your loss. I hope you are taking care of yourself and getting regular checks for yourself so if you develop bc, it can be caught early. Be sure to stay in touch with friends and encourage them to get checked also. I think it is healthy to mourn your sister's death although you should not allow yourself to become depressed but instead celebrate and embrace the good times you had together.
There are many ways to keep your memories alive and honor her life by getting together a team of friends and family to walk/run in her name in the relay for life or Susan G Komen race for a cure. The great thing about the relay for life is that while you are sitting and waiting for your turn, you can share great stories about times you had together plus listen to others tell their stories of how your sister impacted their lives.
I hope you can take comfort in knowing that you are not alone.
TAM