Cecilia began her career with the Oklahoma Department of Human Services  (OKDHS) in Oklahoma County 55C in 1971 until 1981 when she moved to the 55A office. She worked in almost every program area and served as the assistant to many county directors, supervised the office support staff and interpreted for the Spanish speaking clients during those first 28 years. 

Tannehill joined the State Office Policy Management Unit in 2000 where she worked with policy, Section 8 Homeless applications and performed administrative support duties. In 2002, she joined the OPPR unit where she assisted with research support, data inquiries, policy distillations, Oklahoma Human Services Foundation accounts, Spanish interpretations, finance budget, personnel and payroll. 

Tannehill currently serves as the principle assistant to the CIO and this involves managing the overall day to day operations of the OPRS office and assisting the ISD staff. She serves as a board member for a homeless program for high school kids and is actively involved in the local Hispanic community.