Mrs. Which first appears at the end of Chapter 3. She is the wisest of, and the clear leader of the three women, and upon appearing, immediately demonstrates her vast knowledge of understanding in tesseract travel. Her distinguishing quirk is her long, drawn-out method of speech, symbolized by doubled and tripled consonants in her words (as in; "Nnoww, cchilldrenn, yyou musstt nott bee frrightennedd att whatt iss ggoingg tto hhappenn,"). She is the one who usually provides the group, most especially Meg, with the clues the children need to solve the problems encountered during their travels.
In the 2018 movie, along with the other Mrs., Which's dresses often change, first starting with her earth dress, which consists of a silvery torso and and dark gray skirt which is finished off by a half-circle shape at the bottom. Her outfit is completed with a circular bun in her hair, followed by a few loose strands. Her next outfit, at Uriel, is an outfit that has a top with golden sleeves, a golden bodice with black and orange stripes, and a bubble-like skirt, and is finished with a half-crescent shaped hairstyle. Mrs. Which's third outfit, which appears on her at Orion, is started with a long, silver braid, and followed by a silver, papery top with a plain, brown top. Her last dress, the one that appears at Camazotz, home of The IT, appears a lot like her earth outfit, except slightly different. For instance, her dress at Camazotz has her hair down, and is a darker color. It also consists of a wire tube circling around the back of her neck. Most of Mrs. Which's oufits have her eyebrows beaded or pierced.
In the book, her physical appearance is not set; she appears as a shimmering light most of the time. However, she does once take on the appearance of a traditional witch, complete with black hat and broom. She does not stay long in this form, though, as corporeal appearance is quite difficult for her to maintain.