The text straight-up describes what's going on from Meg's perspective, without much in the way of literary flourishes. The heavy use of dialogue adds to this sense that we're right there with Meg as she undergoes her adventures. Here's an example that combines those stylistic approaches, from Meg's return to consciousness on Ixchel:
The first sign of returning consciousness was cold. Then sound. She was aware of voices that seemed to be traveling through her across an arctic waste. Slowly the icy sounds cleared and she realized that the voices belonged to her father and Calvin. She did not hear Charles Wallace. She tried to open her eyes but the lids would not move. She tried to sit up, but she could not stir. She struggled to turn over, to move her hands, her feet, but nothing happened. She knew that she had a body, but it was as lifeless as marble.
She heard Calvin's frozen voice: "Her heart is beating so slowly–"
His words no longer sounded to her quite as frozen. Was it his words that were ice, or her ears? (10.1-2, 19)
By focusing on Meg's basic sensations from the inside, without explaining their cause or how she appears to others, the text places us inside her body, straining as she is to try to figure out what's going on. Calvin's voice is described as "frozen," but we learn, as Meg does, that she's the one who's frozen. By simply ticking off Meg's sensations and giving no more information than what is available to her at that moment, the text places the reader in the same position as Meg, dealing with her sense of confusion.