Theis chairs the Senate Insurance and Banking Committee and Senate Education Committee, and is vice-chair of the Senate Regulatory Reform Committee. She also serves as a member of the Economic and Small Business Development; Health Policy and Human Services; Joint Committee on Administrative Rules (JCAR); and Oversight committees.

Theis first began serving as the 42nd District State Representative in 2015. She served two terms, until being elected to the 22nd District State Senate. While in the House of Representatives, Senator Theis served as Chair of the House Insurance Committee, Vice-Chair of the House Judiciary Committee, and served as a member on the House Regulatory Reform, Law and Justice, Local Government, and Oversight and Ethics, and Financial Service committees.

Prior to her election to the House, she served as Brighton Township Treasurer from 2008-2014. During that time, she served as chair of the Brighton Area Fire Authority, the Livingston County Republican Party, and the Livingston County Treasurers Association, and was a member of the Brighton Township Planning Commission.

Theis graduated from California State University, Fullerton with a bachelor's degree in Biology and a minor in Chemistry.

She and her husband Sam have two children and one grandchild, and they reside in Brighton.