In 2 seasons with MNU, Costa pitched pretty much every other game, and played Gold Glove defense at third, short, and second in the other games. She transferred in from San Joaquin Delta College, and in 2010, she was named Conference Pitcher of the Week 4 times, including 1 National Pitcher of the Week, Conference Player of the Week twice, 1st team All-Conference (officially as a shortstop), Conference Newcomer of the Year, and Conference Player of the Year. In the circle, she went 21-4 with a 1.56 ERA, a .157 opponent batting average, and 235 strikeouts in 152.1 innings. In 54 games at the plate, she hit .472 with 17 doubles, an MNU single-season and career record 17 homers, 56 RBIs, a .907 slugging percentage, a .534 on base percentage, and a 1.441 OPS. Her 2010 offensive season dwarfed any other in MNU history, but so did her 2011 season. In the circle, she went 16-3 with a 1.70 ERA, a .198 opponent batting average, and 152 strikeouts in 119.2 innings. In 51 games at the plate, she hit .487 with 13 doubles, a nation-leading 28 homers, 76 RBIs, a 1.135 slugging percentage, a .547 on base percentage, and a 1.682 OPS. She was named Conference Player of the Week twice, 1st team All-Conference, Gold Glove (at the ambiguous INF position), Conference Player of the Year, and 1st team NAIA All-America. She was runner-up for National Player of the Year, and MNU went to Nationals for the 2nd year in a row.