WASHINGTON - A Mississippi woman pleaded guilty in federal court on Tuesday to trying to join Islamic State in Syria, 2-1/2 weeks after her husband entered the same plea.

Jaelyn Delshaun Young, 20, was arrested at a Mississippi airport in August 2015 while attempting to board a flight to Turkey with her husband, Muhammad Oda Dakhlalla, 23.

Young acknowledged her role as the "planner of the expedition" in an incriminating farewell letter, according to court documents filed by US prosecutors. Convictions for Islamic State-related activity by Americans have become more frequent in recent months as more than 80 such cases brought by US prosecutors since 2013 work their way through federal courts.

Young's Twitter posts about her desire to join the militant group caught the attention of the FBI in May 2015, and an agent posing as an Islamic State recruiter began corresponding with her and Dakhlalla. Young and Dakhlalla told the supposed recruiter they would help Islamic State "correct the falsehoods" about it in US news media, such as reports that the group trades young girls as sex slaves, according to court records.

Both Dakhlalla and Young, of Starkville, Mississippi, are US citizens. Young converted to Islam in March 2015, the court documents said.

The couple entered their guilty pleas in the US District Court for the Northern District of Mississippi, in Greenville.

In exchange for Young's guilty plea to a single count of conspiring to provide material support to a designated terrorist organization, which carries a maximum sentence of 20 years in prison, US prosecutors agreed to not press any other charges.

According to court records, the couple, who had an Islamic marriage but did not get their union legally recognized, were motivated to join the group after viewing Islamic State executions of people they deemed immoral, and because they perceived the group as "liberators" of parts of Syria and Iraq.