Jury selection in the case against Frances Dingle had been scheduled to get under way in Macomb County Circuit Court.
Instead, Dingle offered the plea to the murder charges as well as to four counts of operating while intoxicated causing death.
A no contest plea in Michigan is not an admission of guilt but is treated as such for sentencing purposes.
Dingle's lawyer, Michael Dennis, told the court she was pleading no contest because she had a "lack of recall" of the events of the day of the March 2009 crash that killed Devon Spurlock, Erica Haudek, Jordan Michalak and Stephanie Currie.
"We'd all like to see a guilty plea," Macomb County Prosecutor Eric Smith said afterward, but "the most important thing is she took responsibility today."
Dingle faces a minimum of 19 years in prison for each murder count when she is sentenced May 19.
Dingle's blood-alcohol level after the crash was 0.16 percent, twice the state's legal limit. A police officer who interviewed her at a hospital said she had skipped an Alcoholics Anonymous meeting that day and bought vodka and beer with a friend.
The teens, who ranged in age from 15 to 19 years old, were in a car waiting to cross the road when it was struck by Dingle's van.
Assistant Prosecutor Bill Cataldo has said she turned it into a "missile."
Three of the four victims attended Lake Shore High School in St. Clair Shores.