What's the right thing to do when you are faced with a family member wanting back in your life?

This is a long story, I will try to shorten it up as much as possible. Its about my grandmother, she isn't the best person in the world. She is nice and can be sweet at times. She is talkative and overbearing. She is selfish and judgemental. She can also be hateful and downright cruel. You see, she only had one son, who is my father. My brother and I are related to her by BLOOD. She divorced my grandfather a long time ago and married another man. This man already had his own children and their offspring she treated like her own. She did everything in her power to make them her grandchildren. She tried so hard to be accepted into their family and she was. After this happened, my brother and I were shot down to second place. She always put them first. She went to all of their parties and baseball games. She attended every graduation and important events in their lives. The woman lived 3 hours away from us and the other grandchildren, yet she still found time to be with them. As I recall, she only went to 1 of my birthday parties, and that was BEFORE the other grandchildren were born. She never went to any event that me or my brother had. Growing up she always nagged my brother and I about sports and how we should join...blah blah blah. She wanted us to join because she didn't think we were good enough. My brother and I aren't really made for sports. We're both genius's and we have accepted that. We have never been popular, we have always been opposite and that has always bothered her. The other grandchildren are beautiful. They have long blond hair and blue eyes. The boy is captain of the football team, the girl is captain of the cheerleading squad. They are both idiots. She chooses them over us. She threw out her own grandchildren for two bleach blond morons. I can't go on much more or I'll get really pissed because it gets much deeper than this. Anyway, she eventually stops speaking to us altogether. She completely ignored us and pretended we never existed. She made her choice. Her husband died a few months ago and now she is no longer connected to the other grandchildren. She rarely sees them, now she feels awkward and uninvited into their lives because she is not blood. Now she wants back into our lives. I am very very angry at her, but she is my family and somehow I still ******* love her. I don't understand why I still have feeling for her after what she did to us, I am so mad, yet I wonder what the right thing to do is. Should I forgive her and receive no satisfaction in rejecting her like she did me? Or should I not forgive her and tell her she can go to hell? I am conflicted because I just don't know what I should do. I really would like to just ignore her and tell her to **** off, but I still love her and I want to forgive her. She hurt me so badly I just don't know if I can. I feel two different ways about this. I just want to make the right choice. I am a Christian, I am scared if I make the wrong decision how I will feel about it for the rest of my life. One way or another, I will either Regret for the rest of my life Ignoring her, or I will regret for the rest of my life forgiving her. Please help me. I'm sorry this was so long, I wasn't planning on it being this much. I'm so sorry. Thank you for reading this. I'm so so sorry for its length :(