Callsen grew up in the Virginia school system. She completed her undergraduate degree at Yale in 2008, then taught seventh-grade math for two years at a KIPP Academy charter school in Lynn, Massachusetts with Teach for America’s Boston Corps.
Callsen completed some coursework for a master's degree in education at Boston University while she earned a Massachusetts teaching license in middle school math and science.
She moved to Charlottesville in 2011 to attend the University of Virginia School of Law, from which she graduated in 2014. Since moving to Albemarle, she has participated in the School of Law's Child Advocacy Clinic, which offers legal representation to low-income children in Virginia.
Callsen currently resides in the Agnor-Hurt Elementary district with her husband and her two sons. Her husband is co-founder and CEO of Rho AI, a predictive analytics startup that computes real-time strategy for NASCAR drivers. 
Callsen announced her candidacy for the Rio District seat on the Albemarle County School Board on April 19, 2017 at Pen Park. She defeated former Agnor-Hurt Elementary literacy instructor Mary McIntyre in the November election, capturing 63 percent of the vote.
Callsen succeeded Pam Moynihan as the Rio District representative. Moynihan decided not to seek a fifth term on the school board in 2017.
|Source: Albemarle County|
Callsen has said she will focus on closing the disparity of learning levels between students in Albemarle County, reducing overcrowding in schools in Albemarle's urban ring and finding long-term districting solutions for the division. Callsen also wants to ensure that all schools have access to and are offered equal resources.
- Web. Former teacher, UVA Law grad enters county School Board race for Rio District, Charlottesville Tomorrow, April 19, 2017, retrieved April 23, 2017.
- Web. Albemarle School Board votes 4-3 to move to Stage Three, Katherine Knott, Daily Progress, Lee Enterprises, October 8, 2020, retrieved October 15, 2020.
- Web. Albemarle County, Virginia State Board of Elections, retrieved November 8, 2017.
- Web. 2021 November General Election Results - Albemarle County, Virginia Department of Elections, retrieved December 9, 2022.