What can i do to help a sad friend?

Honestly.. uming you are good friends with her, you know what kind of stuff she likes in terms of food, candy, soda/drinks, movies, etc... If you are going to be hanging out with her soon, just get her some candy, favorite drink, that kind of stuff... grab one of her favorite movies.. When you see her, you give her a big big hug.. No need to even mention that her dad ped away.. She knows.. She knows you know.. And she knows you're sorry. She may want to talk, she may not, but let her bring it up.. Try to be Friend cheer her up ( but not too much :p ) and just be there for her.. So she knows she has people there. It's much better to show her youll be there for her and supporting her rather than just saying it.