Hello J..
I think something like this (or at least as scary as this) has happened to every mother. The important thing to focus on is your baby is OK.
Just like you, my son slept in the bed with me when he out grew the bassinet and I was not ready to put him all the way down the hall in his crib yet (my husband worked nights, so it was just the baby and me in bed). When he was about 4 months old, he rolled off the bed one morning. I cried and cried, too. I felt like a bad mother, thought about what "could have" happend, and long after he stopped crying, I was still crying.
My grandmother tells a story of how her 1st child fell of the couch at 6 wks, her 2nd fell off the couch at 4 wks, and her 3rd fell of the bed at 2 wks. (She said she never had a 4th because she was afraid it would fall off the delivery table!)
It is always scary when something happens to your child (especially when they are that little) and you will always be upset or feel guilty, especially when you feel it is your fault or you could have stopped it. My son is now 2 and since the bed incident he has fallen off his changing table (with me standing right there!), fallen down learning to walk and gotten hurt doing various things he wasn't supposed to. It may not be a comfort, but she will probably have a few more minor "accidents" in the coming years. I know my son has. Sometimes you can prevent them and sometimes you just have to be there with an ice pack. It is part of childhood, and although it always hurts me when my son hurts, I know how to handle it better now. "Oweys" may slow him down a bit, but he is up and moving a second later.
You should not beat yourself up over it, like I said, it is important to remember that you daughter is OK!!!! You are a good mother with good motherly instincts (I know that because your instincts allowed you to do that superhero twist to land on your back without knowing how!) Don't focus on what happend or what could have. You baby is OK, and that is the most important thing.
God Bless!
M.