Seeking for Good Deeds

My sister took her own life 4 1/2 years ago. I heard from the Mahayana nuns that people who took their own life will definitely go to hell and have to suffer for a long time. These people will require to receive a lot of good deeds in order to pull themselves up to the top. My sister used to make donations to some charitable organisations. In order to help my sister, I continue the act for her and trying my best to make donations within my means. I hope by doing so, she will not have to suffer and can quickly move on her life to another world. Am I doing the right thing? May the Triple Gem help my sister so that she can be happy again. Sadhu Sadhu Sadhu!!!