Krieger played collegiately for the Penn State Nittany Lions, where she was named a first-team All-American as both a midfielder and defender.

She represented the team at three FIFA Women's World Cups: 2011 in Germany, where she played every minute of the tournament and reached the final; 2015 in Canada, where she started every match as part of the defense that held opponents scoreless for a record 540 minutes and helped lead the United States to become champions; and 2019 in France, where she made three appearances as the United States defended their title.

A few months later in January, after traveling to visit her family, Krieger began experiencing shortness of breath and checked into the hospital as a precaution.

She was required to do a series of self-injections of enoxaparin for several months, but eventually made a full recovery and joined the Nittany Lions for her senior season.

[9][16] Penn State earned a No.2 seed at the NCAA Tournament and made it to the quarterfinals, when they were defeated by Notre Dame on November 24.

[15] Updated through July 28, 2016[9] Following her freshman year at Penn State, Krieger joined the Washington Freedom for exhibition matches in the summer of 2004.

[19] Following her short time with the Northern Virginia Majestics in the summer of 2005, Krieger returned to the Washington Freedom in July 2005 for more exhibition matches with the team.

[21] In November 2005, Krieger sustained a broken leg while with her collegiate team and eventually developed a pulmonary embolism, which kept her off the pitch that summer.

In order to recover and refrain from further traveling, Krieger remained at Penn State and did not join the Washington Freedom for their 2006 season.

[4] Krieger made her first appearance for the Washington Freedom in the 2009 WPS season on June 13 in a match against the Chicago Red Stars.

[31] In January 2012, Krieger sustained a serious knee injury while with the United States national team that kept her off the pitch for the rest of the season.

[31] In December 2012, Krieger requested and was granted release from her contract in order to play in the newly formed National Women's Soccer League.

[37] In August 2013, it was announced that immediately following the NWSL regular season, Krieger would be joining Tyresö FF in the Damallsvenskan, the highest division of women's soccer in Sweden.

They joined other United States national team members Christen Press and Meghan Klingenberg, who were already with the club on long-term contracts.

During the team's league opener on April 10, 2015, Krieger suffered a concussion in the 17th minute after making contact with the head of Jessica McDonald as they both jumped for a header.

She joined national team players Alex Morgan and Ashlyn Harris, who had also previously played with the Spirit until the 2015 expansion draft.

[54][55] Prior to the 2018 NWSL season, Krieger signed a contract to remain with the Orlando Pride as she was no longer allocated by U.S Soccer.

[84][85] In the team's final group match on March 7, Krieger recorded her first assist and helped the United States defeat Finland.

[4] Krieger made her return to the national team in January 2013, when she was called up to a 29-player training camp leading up to two matches against Scotland in early February.

[131] Krieger joined the national team for a training camp at the end of August in order to prepare for two matches against Mexico in September as well as the 2014 CONCACAF Women's Qualifying tournament in October.

She played all 90 minutes to help the United States advance to the final and qualify for the 2015 FIFA Women's World Cup.

[147] Krieger made a key save during the team's first match on March 4 when she blocked a shot by Norway's Emilie Haavi.

[153] Krieger joined the national team on a Victory Tour following their World Cup win that started in Pittsburgh, Pennsylvania on August 16 and ended in New Orleans, Louisiana on December 16.

[157] The United States qualified to the 2016 Olympic Games in Rio de Janeiro after a semifinal win against Trinidad & Tobago on February 19.

She replaced Crystal Dunn in the 70th minute to help the United States secure their first-place finish in the group with a 1–0 victory over France.

[176] Krieger made three appearances during the tournament including as a halftime substitute during the final against the Netherlands as the USWNT won 2–0 to successfully defend its World Cup title.

[184] In June 2015, Krieger became an ambassador for the non-profit organization Athlete Ally, which works to end homophobia and transphobia in sports.

Krieger, who earned her U.S. Soccer "C" license following the course, has expressed interest in coaching at the professional or national team level.

[190] Following the concussion she sustained while with the Washington Spirit in April 2015, Krieger teamed up with Unequal, which makes protective sports gear.

Harris is also a soccer player who played with Krieger on the Washington Spirit, Orlando Pride, NJ/NY Gotham, and the national team.