Tennell won her first competition when she was ten years old. In 2010, at the age of 12, she came in first place at the Upper Great Lakes Regionals, which qualified her to compete as a juvenile at the 2010 U.S. Junior Nationals, where she came in 10th place. Her goals for the following season was to perfect her double axel and return to junior Nationals. In 2011, she came in third place in the intermediate division at the Upper Great Lakes Regionals, and 15th place at the U.S. Junior Championships, again as an intermediate. In 2012, as a novice, she came in third place at both the Midwestern Sectionals and 2012 Upper Great Lakes Regionals. She competed, also as a novice, at the 2012 U.S. Championships in San Jose, California, where she came in tenth place overall, after earning 32.60 points and coming in tenth place in her short program and 68.78 points in her free skate. She later told a reporter that she almost got lost getting to the event, and began her short program on the wrong side of the rink because it was the first time she skated in a big stadium and there were no lines or hockey circles on the ice like the on rinks she was familiar with.