When I was younger I watched all the old reruns on TV Land. There was a black and white episode about a robot/alien that was friends with a little girl. He was taking lots of blood from her every time she visited, in a spherical ball like glass container. Eventually the father/mother finds out what is going on and kills the alien/robot/monster, but comes to find out he was taking blood to save the human race and just doomed everyone. I am dying trying to figure this out. Any help would be appreciated. Thanks!
Minus the part about the alien taking blood, this sounds a bit like The Twilight Zone episode The Gift. In it, it's a boy, not a girl that befriends an alien. People from the boy's village kill the alien, only to find out that he was on Earth to
Deliver a cure for cancer.