Damn, I just feel so deeply for your pain. You have to know that you did the best you could and you made the right decisions. Your mom had her own will in what she decided to do and there was nothing you could do to stop it. I don't know how you live with that, but I am sure you will find a way to make peace of it. I say I don't know, but I really do. My son committed suicide and I know the depths of pain involved. It is just so hard and I feel for you.
My mind knows I did the right thing but my heart feels that I should have tried harder.
Let you mind win this one. It is able to reason better; our hearts make the struggle all that much greater.
Your daughter is understandably having a hard time. She doesnt know why grandma would leave her. She is probably dealing with her own issues of guilt and doesnt even know it.
The thing that helped me the most was going to a suicide survivors support group. It was so good to be able to talk to others who truly understood. It was refreshing in a way and the problems in trying to talk to people who dont get it vanished in the group. I would suggest you try that and take your daughter if you feel she is ready.
There are tons of great books out now, too - even some for teens dealing with it. Just keep talking to her. Don't assume she is ok, even after a few months. The suicide rate is very high for immediate family members and close friends after a loved ones suicide. All of you are at high risk, so make sure you know that.
You might also talk to the school counselor and her teachers. They need to know how difficult this is for your daughter and they need to ask her how she's doing and make sure they dont ignore it. When my youngest returned to school (high school) after his brother's death, everyone acted like nothing happened. It made it unbearable for him - all the pretending that everything was fine. He wrote an essay about it a few years later and until I read it, I had no idea how bad it was at school.
Those are my thoughts for now. I have a ton, of course, about this issue, but this will be enough to think about.
I am so heartbroken for you.