What a terrible, terrible thing. I don't want to say something that's "boxed" for things like this, such as "I'm sorry for your loss". That won't even BEGIN to say how truly sorry I am, for you and your whole family.
If nothing else, I'm glad that the people she loved the most were with her when she died.
I am sorry I did not see this sooner. I am so sorry to hear this. What a senseless tragedy. Please know that your family is in our thoughts and prayers.