Why must Meg go alone to Camazotz? How is her relationship with Charles Wallace important to her ability to free him?

Meg has to
venture alone to Camazotz to free Charles Wallace because she knows him better than anyone
elseand more importantly, he knows her. Mr. Murry has been away so long as a prisoner on
Camazotz that he hardly has any relationship with his son, and Calvin has only been a friend of
the Murry family for a short time. Meg realizes this herself, saying,

[I]t has to be me. It can't be anyone else. I don't understand
Charles, but he understands me. I'm the one who's closest to him.