1) When filling out a history section for a non-silent protag/malleable protagonist, only what is present in canon should be included. If you want to include inferences or how you interpret something, make sure to include that modifier within the application ("This is what happened in her history, and based on evidence and actions I believe that this could have been what happened next.")

2) You're free to solidify which of these traits as a zombie are real based on your own judgement and interpretation of the canon! If any of this is debunked based on subsequent games, you can retcon this and we can move from there.

3) That magic is totally fine!