Re: What do I do? I'm a 23 year old orphan.
You have had some terrible losses. I'm so sorry!!!! It sounds as if you are doing all you can for your sister. You love her, you have offered many ways of support, but ultimately it is her life, just as you have your own to live. My suggestion, since you do believe in God, is to consider looking for a Church or temple to attend. In time, they can become like a new family for you. My own Church family is very loving and its been so helpful.
Also, I believe in my heart that God does NOT want you to feel guilty for having good times, knowing that your sister is not. You both need to move forward with your lives, and having good times is a way of moving forward. Your parents would want that for both of you I'm sure.
You sound like a loving and responsible girl, but try not to take on all of the responsibility of your sister, too. We each have free will, and if she is not willing or ready to accept your help, just stay lovingly removed and continue on with your own healing.