She wasnt nonchalant when he died. She was pissed and vowed to find out who murdered him and make that person pay. That emotion was quenched when she learned that Cable killed himself and she became affectionate towards the teen version who is only a few years removed from she was forced to leave him. From that point, grieving older Cable became less of an issue bc she still had him around, albeit at a younger age, but he wasnt truly gone. We saw an insight into her head in terms of Cable's death in the Exterminated issue when she helped Hope through her grief