Part of my training in seminary is walking through grief with others.
I'll start by saying this: everyone grieves differently. They have a different pace of walking through the stages, and show them differently.
I assume by your post that you haven't experience a loss close to you, else you would have more of an idea of what you needed.
I'll start with this: what most people need is presence. It's impossible to know what to do, but being there to listen and walk through their grief is the primary thing we learn to do. Listen to her talk about her father. If you knew him, share appropriate stories about him with her. At this point, don't contradict her; that can come later if at all. She needs you there to be with her.
Some things to avoid saying: "It's all for the best" "He's in a better place now" "It's all part of [whatever belief system you have] plan" "At least he didn't [X]" "Be strong" "You should (or shouldn't) feel [x] now" The best thing that you can say is "I'm sorry. I'm here for you and you really matter to me"
Then, pay attention to her cues. At this time, people are numb and need guidance. Help her by walking alongside her and help her with the decision-making process. There will be a bunch of those to make right now, and she and whole family are hurting.