In 1982, Trainor became the first controller of John Deere Community Credit Union (JDCCU), and since that time, it has grown to be the largest one in Iowa and a top credit union in the nation. Trainor was named president of JDCCU in 1990 and it had $197 million in assets. As of March 30, 2005, JDCCU had more than $1 billion in assets and maintained its capital level at 10 percent, demonstrating her effective management of the credit union's resources.This has created member loyalty with 67 percent of the credit union's members considering JDCCU their primary financial institution, compared with an industry norm of 52 percent.

In addition, Trainor has broken technological ground at JDCCU by introducing e-commerce services such as: home banking, electronic statements, bill payment and account aggregation and in 2003, Trainor implemented balanced scorecard.