Its because before she was transported and read the novel, she called him father . You can see in one of the earlier chapters when he died in the novel, she was crying saying “nooo father” or something
Because the webcomic she was reading before going into that works didn't say the name of that white haired man. They only said he was the father of the make protagonist and that he died of black magic and stuff. Welp. That's what I think at least.
Someone plz explain why she calls him Father.. i cant understand ..