She was elected to the Ontario legislature in the 1985 election, defeating Progressive Conservative incumbent John Williams by over 4,000 votes in the North York riding of Oriole. The Liberal Party formed a minority government after this election, and Caplan was appointed as Chair of the Management Board of Cabinet on June 26, 1985. She resigned her portfolio on June 16, 1986, following accusations of a conflict of interest relating to her husband's business dealings; while protesting her innocence, she claimed she had lost the confidence of the house. Caplan was subsequently exonerated by a parliamentary commission.