Sheena Blackburn, 24, who was arrested with two men last fall for their alleged roles in a string of North Seattle robberies, pleaded guilty today to three counts of second-degree robbery.

Blackburn, who authorities say was the getaway driver, faces a standard range of 15 to 20 months when she is sentenced, said Dan Donohoe, spokesman for King County Prosecutor Dan Satterberg. When she returns to court on Jan. 22 for sentencing, prosecutors will be requesting that she serve 20 months behind bars, Donohoe said.

Blackburn has also agreed to testify against her co-defendants, Jarvis Gibbs and Clovelle Harvey, who are still facing charges in the case. The two men are slated to be tried later this month, Donohoe said.

The three defendants are believed to be responsible for at least some of a string of robberies in Magnolia, Green Lake, Capitol Hill and North Seattle. When the three were arrested police also detained several other people who were questioned and released.

Police said the break in the case came when a credit card belonging to the one of the victims was used at a convenience store. Within a half-hour of the robbery more than $160 in charges were rung up on the man's credit card at a nearby 7-Eleven, police said. Surveillance images from the store were obtained by police and distributed to the media, which led to the the suspects' identification.