Angela, I am so sorry to hear of you loss. It is very difficult to know what to say or do when those special days come along. I also recentlly loss my beautiful grandson to murder. His father murdered him then killed himself. This is my daughters first Mothers day with out him and I was out asking the same question. Every year my children would come over and we would have dinner together because this is what I love most, family time. This year my daughter is not coming. It has been onlly 6 months since my grandson was taken from us. He was her only child and my only grandson. He only spent 22 months on earth but they are packed with beauiful memories. I decide that it was best to just be there to support my daughter. I will call her on moms day and even though Lucas is gone, she's was a wonderful mom and i want her to know that. I know that it is best to give her room but be there for her especially through this special day and i will. If you ever need to talk let me know. I am here. I understand the pain that you and your sister are feeling. My prayers are with you and your family during this very difficult time.
I read your post about your nephew and wanting to comfort your sister on Mothers Day, understandably a very difficult day for us moms. Here is something that came in my email the other day that I hope will help you with some ideas: http://www.griefwatch.com/what-grieving-moms-want-for-mothers-day. You're very thoughtful and your sister is fortunate to have you as part of her support system!