This morning, I woke up to a text message that made me exhale for what felt like the first time in days. “Good news,” it said. “I passed gas.” It might sound small, maybe even strange, to celebrate. But when you’re watching someone you love fight for their life from afar, even the tiniest sign of progress feels monumental. My sister, Laura, has been in and out of the hospital, enduring pain, surgery, and uncertainty.

Taite Koehler of Kitchener, Ont., has made a documentary focusing on five teenagers, including herself, who live with chronic illness. She says she wanted to make the film because she feels like many ...