Why is Meg the only one who can go back to Camazotz to try to save Charles Wallace?

Meg fights the instinct to save Charles Wallace, but as soon as she relents she understands the power of her own gesture. Her gift of sacrificial love is the only thing that can save Charles Wallace. Mr. Murry’s love would not be strong enough, nor would Calvin’s love. It is only because Meg has invested so much of herself in the boy that she is able to save him.