Just try keeping up with Sierra Archer. This smart, sassy eight-year-old always seems to be on the go, whether it’s swimming, playing in the park, dancing in Zumba class, or riding her beloved horse, Pippin.

For Sierra, staying active is one her favorite ways of coping with an inoperable brain tumor, which she’s been fighting for over three years. “Sometimes I get scared about it. But when I can move around, that helps me calm down,” she explained.

Sierra plans to channel her love for animals into a career as a veterinarian someday. Until then, she puts her nurturing nature to good use helping other kids like her. “When I meet a kid with cancer, I tell them to think good thoughts, no matter what,” she says. “That always works for me.”