Most Helpful Girl
Just leave her, she will in time get over it. I think she going through a phase of a big crush. Sometimes a crush take over you, you become possessed by an evil spirit, and we start thinking weird and wonderful things about that person. Having a crush on someone can consume you.
I think your sister has too much time on her hands, just too keep her busy so she will stop thinking about this person. try and take her out to places, invite her friends over more often.
Most Helpful Guy
Jesus christ. A therapist would help.
The age isn't the problem here, it's that she's being unrealistic. This is a celebrity, and she is a nobody. She doesn't actually know him, he doesn't and won't know her, unless by negative association from creepy stalker behaviour, and fixation and thinking there is some possible future is really unhealthy.
It's good fun to have a celebrity crush, I suppose but to realistically think that knowing them is a possibility, and for the thing that worries he to be that he "already" has kids, is really a big red flag. She's out of touch with reality.
I sense an underlying crisis. So, professional help.
Are your parents aware of the severity of the situation?
Lastly, which is it. He's single or he's married.