Crying in front of her will not help! I have never cried over my diagnosis and perhaps that is how your daughter will be! Certainly cry and scream and anything in between in your own space but being composed and practical will go a long way to helping her. Take her cues! From what you say she's had a lot of stress already so perhaps her coping mechanisms are in place ready to roll!
There's no rhyme or reason so as others have said waste of energy going through the what ifs!
Even though you have experienced same I thought I would put up a link to the BCNA website that maybe beneficial for you and or your daughter and a gateway to the BCNA website for further information
https://www.bcna.org.au/understanding-breast-cancer/talking-to-family-and-friends/Take care