After they escape, Meg feels angry at her father and Calvin for not seeming to share her urgency to go back and save Charles Wallace from Camazotz. She is especially angry at her father for leaving Charles Wallace behind.
Some of Meg's intense anger and hostility come from the evil effects of having been on Camazotz. Although she fought off the attempts of IT to control her mind, some of its evil has infected her. As Aunt Beast says:
The Black Thing burns unless it is counteracted properly.
Meg is also an adolescent girl who idealized her father and is now having to come to terms with the idea that he is not perfect and all-powerful. She is angry that he can't simply solve all her problems and save Charles Wallace.
While feelings are feelings, and therefore not able to be delineated as things you "should" or "shouldn't" feel, the novel makes clear that Meg's response is unfair. Her father and Calvin want to rescue Charles Wallace as much as she does. They are trying as hard as she is, but the answers aren't easy. Meg has become temporarily less trusting because of her experience of evil on Camazotz.