Under Miller's leadership, the Progressive Conservatives were reduced to a tenuous minority government in the 1985 provincial election. Stephenson was personally re-elected without difficulty, and was named as Ontario's first female Treasurer and Deputy Premier on May 17. She accomplished little in these roles. Before having the chance as Treasurer to present a budget, the Miller government was defeated by a motion of non-confidence in June 1985, after the Liberals reached an agreement allowing them to form government with the support of the Ontario New Democratic Party. In opposition, she served as her party's Critic for Health. She retired from politics at the 1987 provincial election.