“I give you your faults,” a celestial being called Mrs. Whatsit tells Meg, before sending her off on her quest. Ms. L’Engle’s message is that Meg’s prickly personality, her “two ferocious lines of braces,” her glasses and plain face, are her secret weapons, that a lifetime spent being different is what will give her the strength to resist.

In Ava DuVernay’s much-anticipated Disney movie adaptation of the book, which comes out Friday, Meg is being played by an African-American actress. That’s huge: It’s thrilling, and important, for all children to see a story where a young black girl saves the day.

What’s less inspiring is the Hollywood makeover that Meg’s three mentors received. In the book, their appearances range from frumpy to “little more than a shimmer.” In the movie, they’re played by Reese Witherspoon, Mindy Kaling and Oprah Winfrey, who was cast, Ms. DuVernay has said, not in spite of her celebrity but because of it.

In an interview, the director said that the character of Mrs. Which embodies what Ms. Winfrey has taught over the years “about owning your light and conquering darkness and how we have to power ourselves through this life in a certain way and look out for each other.”

But are young filmgoers going to know Ms. Winfrey as the SuperSoul Sunday light-bringer, the warrior for women who told an exultant Golden Globes audience that “what I know for sure is that speaking your truth is the most powerful tool we all have”? Or will they recognize her as the woman handing out tacos in Weight Watchers ads, above text listing how many pounds each fiesta-goer has lost?

Ms. Sherer, of Weight Watchers, gave a firm “absolutely not” when I asked if the timing of the Weight Watchers announcement had anything to do with the release of the film. But when the board member/part owner/celebrity endorser of a commercial weight-loss program stars in a movie aimed squarely at young women — the same demographic that her program is trying to tempt with free memberships — what’s the message? Is it love yourself, faults and all, or is it that maybe there should be a little less of you to love?