A purported firebrand on Twitter, Keonna Thomas - a Philadelphia woman charged with attempting to join ISIS - remained a cipher in court Friday.

FBI agents allege that she openly dreamed online of dying for the Islamic State, had raised funds to support jihadists in Syria, and had booked a plane ticket in the hope of joining them there.

But as Thomas, 30, made her initial appearance in federal court, dressed in the head-to-toe black burka in which she was arrested, she said little.

Her appearance betrayed even less, with only colorful hiking boots giving the slightest hint of personality for the woman beneath the robe.

But online, prosecutors said, Thomas held little back. Under the aliases "Fatayat Al Khilafah" and "Young Lioness," she allegedly voiced intentions to take on a suicide mission in the Middle East, cemented plans to travel overseas, and struck up conversations with jihadists the world over.

In one Feb. 17 exchange quoted in court filings, a person identified by prosecutors as an ISIS fighter in Syria asked Thomas whether she was willing to take part in a suicide attack.

Her purported reply: "That would be amazing. . . . A girl can only wish."

FBI agents arrested Thomas at her North Philadelphia home Friday, five days after she had allegedly planned to leave the United States for good.

Prosecutors say she had booked a March 29 plane ticket from Philadelphia to Barcelona, Spain, purchased an electronic visa for Turkey, and researched bus routes from Spain to Istanbul, a popular transit point for those seeking to join ISIS.

Her plans were likely delayed, a source close to the investigation said, by the FBI's March 27 raid on her home.

"Had the government not executed that search warrant," Assistant U.S. Attorney Jennifer Arbittier Williams said, "she would have been on that flight to join ISIS in Syria."

At Friday's hearing, Magistrate Judge Lynne A. Sitarski ordered Thomas held pending a detention hearing scheduled for Wednesday. A public defender appointed to represent her during the hearing declined to comment.

At her home, on the 800 block of North 10th Street, on Friday, television news crews surrounded the three-story, brick-front unit festooned with American flags.

A woman who answered the door told a reporter, "Go away. Go away before I call the cops."

Few neighbors said they knew Thomas or her family.

Thomas' arrest comes amid a concerted push by federal authorities to combat what they describe as a "more decentralized, more diffuse, more complicated" homegrown terror threat.

It followed Thursday's indictment of two women in New York City on charges of plotting to build a bomb for a Boston Marathon-style attack.

In February, the FBI arrested three Brooklyn, N.Y., men, one of whom ran kiosks at East Coast malls including one in Philadelphia, over their alleged efforts to join the ISIS fight.

In all, the Justice Department has brought charges against more than 30 people since 2013 for attempting to join or provide support to terrorist groups - 18 of which involved ISIS.

"It involves the potential lone-wolf actor," Homeland Security Secretary Jeh Johnson said at a news conference Thursday at which he discussed the more recent cases. "It involves the effective use of social media and the Internet."

According to court filings in Thomas' case, the Internet was where her passion for militant Islam thrived.

It remained unclear Friday when or how she became radicalized. But prosecutors say she was voicing her support online for the Islamic State, which has claimed responsibility for the beheadings of two Americans, as early as August 2013.

One early posting on Twitter described in court filings pictured a young boy holding weapons. The caption allegedly read: "Ask yourselves, while this young man is holding magazines for the Islamic state, what are you doing for it? #ISIS."

Another, posted in April 2014, contained images of a skull, flames, and a gun. Thomas purportedly wrote: "I need a permanent vacation that can only mean one thing."

Another Twitter user, prosecutors say, responded with a word that means "martyrdom."

Prosecutors say Thomas spread fund-raising pitches for ISIS and struck up conversations with three foreign jihadists. They included an ISIS fighter in Syria, a radical Islamic cleric in Jamaica, and a Somalia-based native of Minnesota, a hub of recent jihadist recruitment in the United States.

"I don't want to say much here," she purportedly wrote to the cleric on Jan. 30 of her plans to leave the country. "As of now I'm still here in the states but will be leaving soon."

In many ways, the case against Thomas resembles the 2009 arrest of Colleen LaRose, a Pennsburg woman whose virulent online postings under the moniker "Jihad Jane" drew the attention of federal investigators even before she flew to Ireland as part of a plot to assassinate a Swedish cartoonist.

LaRose was sentenced last year to 10 years in prison after pleading guilty to providing material support to terrorism.

Thomas could face up to 15 years in prison if convicted.

jroebuck@phillynews.com

215-854-2608 @jeremyrroebuck

Inquirer staff writer Joseph A. Slobodzian contributed to this article.