Christensen was a member of the Syracuse Common Council before being elected to the assembly.[1] She was first elected to the assembly in 1990, defeating Syracuse Common Councilman Joseph O'Hara in the Democratic primary election, and then incumbent Republican William Bush in the general election.[2] She became the first woman from Onondaga County elected to the New York State Assembly.[2]
She was subsequently reelected nine times; her closest reelection was in 2002, when she defeated Republican nominee Bill Sanford, a former Assemblyman, with 59 percent of the vote.[1] Christensen decided not to seek reelection in 2010,[2] retiring to spend more time with her family.[1]
In the Assembly, Christensen was primarily known for her constituent services work, rather than policymaking efforts.[1] Christensen was a principal sponsor of the New York safe-haven law.[1][3] In 2002, Christensen supported the unsuccessful effort of Assemblyman Michael Bragman to oust Sheldon Silver as speaker of the Assembly.[1]