She saw me get hit by her father and she knows that he doesn't always come home. She told me once that "Daddy does not care for us or love us." I asked her if she was worried and she said "No, but I do worry about you."
Now I'm at a point that I want to file for divorce, but I am afraid to take this step because I don't know how it will affect her. How should I approach this issue with her?
You're concerned about how a separation and divorce will affect her, but even more importantly, you need to think about how staying in the current situation will affect her. She has seen you get hit and has said that she worries about you. Is it better to stay in a situation where she will continue to see things and to worry about you, or to be somewhere else where those are not issues?
All parents who are separating or divorcing worry about the effects it will have on their children. But kids handle things well if we take the time to talk with them and explain what is going on (at least, as much as they can understand).
Your daughter does not need to hear details and specifics about your reasons for a separation, but she does need to hear that you will always take care of her, that you are going to make sure that you are both safe, and that you will always love her. Be sure to not promise things that may not happen, such as that she will see her daddy every weekend. Be honest, but share only things that a seven-year-old should hear and be able to understand.
Talk with your daughter's teacher and school counselor and make them aware of a separation if it happens. They do not want to get involved in your family's business, but they do need to know what is going on so that they can support your daughter while she is at school.