This is so stupid. She's going to know he isn't dead when she tries to contact his family and they either tell her the truth, or are in witness protection as well. Or did you tell her that his entire extended family died?
Or she'll talk to another one of his friends for moral support and they'll be like wtf, what kind of a **** would tell you that, he isn't dead.
Either way you screwed up and she will hate you forever.