Twichell is a native of Fayetteville, New York and a graduate of Duke University in 2011. She is the daughter of Terry and Deirdre Twichell. She has three older siblings Brandon, Ryan, and Carly. She currently trains with fellow USA Swimming national team members Chloe Sutton and Christine Jennings at the Mission Viejo Nadadores in Mission Viejo, California.
She teamed with Andrew Gemmell of the University of Georgia and Michigan University's Sean Ryan to record a time of 57:00.6, winning the gold medal at the 5K Team Event at the 2011 FINA World Swimming Championships in Shanghai, China. Twichell also earned the bronze medal in the women's 5K event at the World Championships in a tight race. It was her first international competition.
She won the 5K race at the 2011 USA Swimming National Open Water National Championships in Fort Lauderdale, Florida and finished third in the 10K to earn a spot on the USA Swimming national team. She was also selected as the 2011 Female Open Water Swimmer of the Year by USA Swimming.
Twichell's busy summer of competition also included a third-place performance in the women's 800 free at the 2011 ConocoPhillips National Championships in August. She notched a time of 8:35.20 in the finals of that event to qualify for the Olympic trials next June.