An 18-year-old Lollapalooza music festival security guard has been charged with a felony after prosecutors say she made a false mass shooting threat toward attendees last Friday.

Officials say they traced two messages to Janya B. Williams, who allegedly made posts that described 150 targets and a massive shooting at the 100,000-person capacity event in Chicagos Grant Park, the Chicago Tribune reported .

Prosecutors said she owned up to drafting the messages because she hoped to leave work early.

Williams initially sent her supervisor one of the messages using the phone app TextNow, which caused festival officials to contact the Chicago Police Department and the FBI , according to prosecutors.

Prosecutors said Williams allegedly created a phony Facebook page for Ben Scott, wrote a threatening post, and showed a screenshot of the post to her supervisor.

An investigation into the TextNow message determined Williams was behind it, according to prosecutors.

Williams, a Chicago resident, has been charged with a false terrorist threat and a hearing is set for Monday.

A judge set her bond at $50,000 and she would be subject to electronic monitoring if released, according to Block Club Chicago .