One of Encanto's biggest unaddressed mysteries is whether Abuela has a power and what it is, but one theory provides a clever explanation as to what the character's gift may be. Encanto has been a strong success for Disney in many ways, and one of the film's greatest strengths is how it underscores the value of family by pointing out that every member of the Madrigal family has value, with or without a magic gift. To this end, it's interesting to consider Abuela's role as both the head of the family and the origin of the miracle.
Every character in Encanto possesses a meaningful gift via the miracle that began when Pedro and Alma fled their home and Pedro was killed. For many of the Madrigals, their gift is tied to a central element of their personality: Antonio, who loves animals, can speak to them; Julieta, a caring and supportive mother, heals people with home-cooked food; and Isabela, who behaves like a princess for much of the film, has effortless good looks and the ability to grow beautiful flowers. In each case, it's hard to say whether the family members receive these powers because they match their unique natures, or vice versa. But it seems clear from Encanto's ending, in which powerless Mirabel saves the miracle, that everyone has an important role to play.
In terms of Abuela Alma's gift, then, the film indicates that she may have powers in regard to her stewardship of the magical candle, Casita, the family, and the community. Like Mirabel, Abuela lacks a tangible magical ability like super hearing or seeing the future, but rather acts as the glue that holds the rest of the family together. Abuela's magic lies in how she creates an environment for the other Madrigals to flourish and use their gifts for good.
Abuela herself helped create the family's miracle through her love for Pedro and her desire to find a safe home to raise her children. And in a move befitting Pixar, Encanto makes her the villain of the story while still emphasizing the complexities of her character and showing that she is ultimately a loving and good person who cares deeply about her family. Furthermore, Abuela's power as the keeper of the Encanto is embodied by the magical candle, which wanes when the family is not united, just like every other Madrigal gift also does. While this is a bit harder to grasp than the more straightforward abilities like Camilo's shapeshifting, it actually showcases how Abuela is one of the most important family members because she keeps everybody together. As Mirabel herself says, "we are a family because of you."
It's interesting, then, that Abuela is so hard on Mirabel in Encanto, since Mirabel actually seems poised to take on Abuela's role as the head of the family sometime in the future. As the only two Madrigals without evident powers, Mirabel and Abuela are nonetheless crucial to creating an environment for the other powers to thrive. While Abuela struggles to balance this ability with her desire for perfection, Mirabel helps her refocus her energies in the end, and the Encanto is restored. Essentially, Abuela and Mirabel have the same gift: to bring everyone together with love and support. This is illustrated by scenes like their heart-to-heart by the river, the song "All of You" which Mirabel and Abuela lead together, and even small details like Mirabel and Casita's very close bond. All of these examples allude to Mirabel's ability to one day take on Abuela's gift, her matriarchal mantle.
Thus, while Abuela's potential gift in Encanto is a bit more subtle than her family members', it's still a crucial component of the real miracle, which is the unity of the family. It began with her and Pedro, and it continues through her keeping of the candle and her love for all of her children and grandchildren. And just as Encanto's ending reveals the true nature of Mirabel's magic ability to heal the family, it does the same for Abuela, too.