She served as a Navajo County Supervisor. A Republican party activist, in 2008 she was appointed to the Arizona State Senate following the death of Senator Jake Flake. A resident of Snowflake, Arizona, she first represented the 5th legislative district.
Following her appointment, she was elected in her own right in 2008. In the 2009–10 legislature, she was a member of four standing committees: Appropriations; Education Accountability and Reform; Natural Resources, Infrastructure and Public Debt; and the Appropriations Subcommittee on Health and Welfare. She served as chair of the Appropriations Subcommittee on Health and Welfare for the Arizona Senate.
Senator Allen was a sponsor of a 2012 bill, SB 1127, that introduced shared parenting to Arizona.
After the death of Chester Crandell, Allen was selected to replace him on the primary ballot and was elected to the Arizona State Senate District 6 seat in 2014, taking office on January 5, 2015. Her current term ends January 1, 2017. In the 2015 legislative session Allen served on the Appropriations, Education, Government (Vice-Chair), Rural Affairs and Environment (Chair), Rules, Water and Energy (Vice-Chair) committees. She was selected by her caucus as President Pro tem.
For the 2015-16 term, Allen serves as President Pro Tem and as Chairman of the Senate Education Committee, where she has played a large role in securing major funding increases for Arizona universities and K-12 schools, the passage of Prop 123 ($3.5 Billion increase in K-12 funding over 10 years), and where she was awarded Legislator of the Year by Arizona Community Colleges and Champion of Education by the Arizona School Administrators. Other awards Allen has won include Friend of the Family from the Arizona Family Project and Champion of the Taxpayer from Americans for Prosperity. Allen also has an "A" rating from the National Rifle Association.
During her tenure as a county supervisor, Allen was said to have attempted to interfere with an internal investigation into the conduct of her son-in-law, a detention officer, with female inmates in the Navajo County jail, where he worked. K.C. Clark, the Navajo County Sheriff, threatened to arrest her if she continued to interfere. In March 2015, Allen filed a senate bill that would provide detention officers, like her son-in-law, with greater protections from disciplinary investigations. Allen has indicated that she was made aware of misdeeds within the jail and that she informed the Sheriff believing he would want to know. According to Allen, that is when her son-in-law was targeted and she discovered the Sheriff was both aware of and part of the problems in the jail. The Sheriff (himself a Democrat) has made a number of accusations that outside groups have spread throughout Allen's district in an effort to defeat her in the 2016 General Election. Allen has countered the Sheriff's claims by pointing out that she has the endorsement of a number of police associations.
Speaking at a June 2009 Rural Development and Retirement Committee hearing regarding a uranium mine, Allen said the world was "6,000 years old."
During a March 2015 Senate committee hearing on a bill that would relax concealed carry restrictions pertaining to public buildings, Allen, a member of the LDS Church, suggested that attending Sunday church services should be compulsory for Americans. Arizona state senate Democrat Steve Farley argued that even if church attendance might prove beneficial for society at large, Allen's proposal was a clear violation of separation of church and state laws, including the First Amendment to the US Constitution.