On Monday, her language - which asked voters if the state's law should be amended to "deny" "affordable health care plans through a state based health benefit exchange" - was struck down by a successful circuit court challenge from Lt. Gov. Peter Kinder.
Carnahan's office said on Thursday that they were ready to appeal, but could not get support from Koster's office, which carries the authority to defend the state's constitutional officers.
"Although we strongly disagree with the decision by the Cole County Circuit Court, this office is not in a position to appeal the decision on its own," Carnahan's office said in a statement. "We are disappointed that Attorney General Koster has refused our request to file an appeal."
Circuit Judge Danile Green wrote that a "correct ballot summary" was needed, and declared the new language should say: "Shall Missouri Law be amended to prohibit the Governor, or any state agency, from establishing or operating state-based health insurance exchanges unless authorized by a vote of the people or by the legislature?"
office said that language is "incomplete, uninformative and a disservice