Kat's mom, an angel, gives Casper an hour or so's life after he selflessly sacrificed his own for Kat's father. If Casper had taken that potion he would be alive for real. Heck, if he'd even been just a few minutes faster he'd be alive. Why didn't she repay him with life? Or maybe, since his unfinished business had been his father and he's gone now, she could have helped him ascend to Heaven for such an amazing act of selflessness? Instead he gets to live for an hour tops before effectively dying and being a ghost again. All in all, she seems like a bit of a cow really.