A California woman who pleaded guilty to planting notes threatening to kill Americans aboard a Hawaii-bound cruise ship, forcing the vessel to be diverted, was sentenced Monday to two years in federal prison.

Kelley Marie Ferguson (search), of Laguna Hills, was given the maximum sentence allowable under federal guidelines, which is determined based on criminal history and other factors. The charges were punishable by up to 20 years in prison and a fine of $250,000 under the USA Patriot Act.

Ferguson, 20, will begin her sentence Nov. 4 for penning notes threatening that Americans would die if the Royal Caribbean's Legend of the Seas (search) stopped at a U.S. port.

U.S. District Court Judge Helen Gillmor (search) also ordered Ferguson to three years of supervised release after she finishes her prison sentence and a psychiatric evaluation and counseling, if needed.

"I do believe you're a troubled individual," Gillmor said.

Ferguson, who hid that she was pregnant at the time, told authorities she carried out the hoax in hopes of diverting the ship and cutting short a family vacation to return home to her boyfriend.

In asking the judge for leniency in sentencing, public defender Loretta Faymonville said Ferguson's threat was not driven by political or financial reasons. Faymonville said her client was "very, very sorry."

"It was done without malice or intended to hurt anyone," Faymonville said. "She was pregnant. She was scared. She wanted to go home."

Prosecutors said the offense was serious, something the sentence should reflect.

"When you undermine the safety people have, either in their homes or when they travel, those people are victims -- whether it's a hoax or not," Assistant U.S. Attorney Ken Sorenson said.

Gillmor agreed, saying the offense can't be blamed on "youthful folly and naivete."

"This is no small prank when you interfere with 2,000 lives," the judge said. "If it seems long, just think about the people on the cruise ship."

Ferguson showed no emotion as the sentence was given and refused to make a statement in the courtroom.

"I was disappointed in that," Sorenson said. "She had an opportunity to let people know she was truly sorry for what she had done, but she didn't take advantage of that."

Following the sentencing, her parents and attorney exited the federal courthouse through the basement, avoiding reporters waiting outside the front doors.

Ferguson was arrested April 26. As a condition of her release to her parents' home, she was ordered to wear an ankle bracelet that monitored her location 24 hours a day with global positioning system technology. She gave birth to a girl on June 25.

The Legend of the Seas was en route to Hilo from Ensenada, Mexico, when the two notes planted by Ferguson were found in a public restroom, forcing the ship's rerouting to waters off Honolulu.

The first handwritten note read: "I HAVE BEEN SENT ON A MISSION TO KILL ALL AMERICANOS ABORD LEGEND IF WE PORT ON AMERICAN SOIL." The second message reiterated the threat.

The notes prompted an intense investigation aboard the ship with 40 bomb-sniffing dogs and more than 120 members of the FBI's Joint Terrorism Task Force searching for biological, chemical, radiological and explosive weapons.

The cost for the U.S. Coast Guard's portion of the investigation alone was reported at $336,000.

Federal agents were in the midst of examining luggage and interviewing the ship's 2,400 passengers and crew when Ferguson admitted to writing the notes, prosecutors said.