If A Wrinkle in Time was, for a long time, considered unfilmable, characters like Aunt Beast are the reason why. An unfathomable alien creature who bonds with Meg and nurses her back to health, Aunt Beast is a fan favourite, but her exclusion from Ava DuVernay's film is understandable. However, up until fairly recently, she wasn't excluded at all.
Talking to Cinema Blend, screenwriter Jennifer Lee discussed the value of Aunt Beast and the ultimate decision to cut her, citing the importance of dialling into Meg Murry's arc as the reason why:
I'd say Aunt Beast was in there until a few months ago, so Aunt Beast did not go lightly. We all fought for her, including Ava, and it wasn't that we were fighting any one entity saying [sic] couldn't do it. We were fighting to try to make it work for ourselves. But the truth was what it did in the book for Meg that it could do, took away from the journey that needed to happen in the film. In the book, she's guided. It's lessons she's learning along the way. It was beautiful entities that are nurturing. Here we had a girl who's about to go in to face, the ultimate, The It, and we really need to arm her with nothing. She had to go in there as raw and as wounded and in feeling the wounds of her father. That moment of finding him and realising he's not the answer to everything and that the pain is still there. Her brother is still in trouble and she's the only one who can fix it and not being armed with all this support before she walked in because that's not what you get in life. So in some ways when we watched it without, we realised it was the right journey for the film, but I still carry Aunt Beast with me because she was my favourite, but I get it.
That's compelling reasoning. In the book, Meg's journey has the space to be complicated and progressive in a way that didn't quite work on film. Still, Aunt Beast is missed.