Sabrina and Tim Mattis say medical cannabis has been a game changer for their 9-year-old daughter Krystal, who has autism spectrum disorder and epilepsy. They were eager for her to try school full-time this fall after years of half-days in school because of extensive speech, physical, and occupational therapies consuming a lot of her time. But that was short-lived, they told WCCO in an interview Thursday, because district officials said she couldn’t take a mid-day…