Katherine Abughazaleh , better known to her fans as Kat Abu, was glowing. It was Monday afternoon, about five hours after Fox News made the shocking announcement that its flagship host, right-wing superstar Tucker Carlson , was leaving the network , and she was making no attempt to hide her glee as we talked over video chat. “I’ve been very joyful today,” she said. “I feel like everyone’s just having a fun day.”  For the past two years, Carlson and his show have been a huge part of her life. The Washington, DC–based Abughazaleh is a senior video producer for Media Matters for America, a not-for-profit media watchdog group, and her job requires her to tune into Fox News’s primetime hours every weekday.   Her Twitter bio used to read “I watch Tucker Carlson so you don’t have to.” At the time of our interview, it was “LMAO.” Abughazaleh, 24, has parlayed her familiarity with Fox News into social media stardom across multiple platforms.…