With credit for time served, 36-year-old Briana Waters of Oakland, Calif., will return for 11 months. The first half of the remaining sentence will be served in prison and then a halfway house.
Waters will report to federal prison after Labor Day, a special request granted so she can be with her daughter the summer.
The sentencing comes after she pleaded guilty to arson and related charges in a plea deal. A jury convicted her in 2008, but that verdict was overturned on appeal.
Waters briefly spoke at Friday's sentencing, saying she's "really, really, really sorry" - through tears - for what she's done.
She said she has "so much regret and remorse" for all the suffering she caused and "wants to be a better person in this world, especially for her daughter."
"This is no one's fault but my own," she said.
Three other defendants were convicted and a fourth killed himself in jail.
The fire at the UW's Center for Urban Horticulture in Seattle caused $6 million in damage. Members of the Earth Liberation Front mistakenly thought a researcher was genetically altering poplar trees.
The firebombs were built at Waters' home in Olympia where she was a student at The Evergreen State College.