Leffler had a record setting weekend in the pool for William Smith at the 2018 Liberty League Swimming & Diving Championships. She broke the school record in the 100-yard backstroke three times and the school record in the 200 backstroke two times and helped the 400 freestyle relay break the school record in the last event of the meet. On Thursday, Leffler broke her first record of the weekend with a :59.21 backstroke split time as the leadoff leg in the 400 medley relay. The next morning she dropped one-hundredth of a second off the time to qualify for the Championship final with a time of :59.20. That evening, Leffler touched the wall third with a time of :58.80. Saturday she took nearly two seconds off the school record in the 200 backstroke in two swims. In the morning prelims, Leffler touched the wall with a time of 2:08.30, a second faster than the previous school record. In the championship final, she finished fourth, stopping the clock at 2:07.22.
