At fourteen, she began playing at third base in the St. Louis Amateur Softball League since other opportunities at school were limited.

Over the twelve years of history of the league, the rules were gradually modified to more closely resemble baseball.

[6] In her rookie season, Bergmann posted a 15–16 record and a 2.05 earned run average in 35 pitching appearances, top numbers for the sixth-place Lassies.

Her biggest thrill in her season debut came when she belted her only career home run in the top of the ninth inning of a game against the Rockford Peaches.

[6] In 1947 the AAGPBL moved its spring training camp to Havana, Cuba, and Bergmann was one of the two hundred girls who made the trip.

She ended the season with an 11–10 mark and a solid 1.74 ERA in 27 games, helping the Lassies win the pennant.