What does Meg realize after talking with Calvin in A Wrinkle in Time?

Your
question must refer to a specific time Meg talks with Calvin during , but
without more specific information I must assume that you mean when Meg talks with Calvin while
they are on Ixchel being cared for by Aunt Beast. At this point, Meg realizes that Calvin loves
her. Even though Meg has always known she loved her family (her mother, her father, Charles
Wallace, and the twins), she has never been able to pin down the power of love elsewhere in the
world until now. In fact, this confession of love by Calvin is the first time that Meg truly
recognizes the power of love from many characters in this novel. For example, Meg now has love
for Aunt Beast, the alien being who saved her from IT. Aunt Beast also loves Meg. It is around
the same time that Mrs. Whatsit talks about her own love for Meg and mentions that Mrs. Who also
shows love in a different way: by providing inspirational (and often biblical) quotes. This
declaration of love from Calvin, the catalyst for the full revelation, is vastly important to
strengthening Meg before she returns to Camazotz to fight IT.