REDWOOD CITY — Videos allegedly depicting a 49-year-old Redwood City woman engaged in sexual acts with a 14-year-old female relative have landed the former behind bars, authorities said.

Dawn Giannini, a substitute teacher who previously taught in Palo Alto and Redwood City, was arrested Oct. 18 after one of the victim’s classmates at Woodside High School viewed the videos on the pornography website PornHub and reported them to the principal. The principal in turn contacted the San Mateo County Sheriff’s Office.

Giannini is charged with 24 felony counts, including lewd and lascivious acts on a child ages 14 or 15, forcible sexual penetration and incest. She has not entered a plea.

Prosecutors contend Giannini engaged in a sexual relationship with her relative from Nov. 21, 2014, to Nov. 20, 2015, when the victim was 14. The victim filmed the alleged conduct with her cellphone and those videos were ultimately uploaded to PornHub. The video sharing site is among the 50 most-visited in the world.

Related Articles `The Great Debaters,’ `Indiana Jones’ set highlight new DVD releases District Attorney Steve Wagstaffe said the majority of the alleged crimes occurred at the family home in Redwood City and during a trip to Santa Cruz.

Giannini previously worked for the Redwood City School District and St. Elizabeth Seton School in Palo Alto. It wasn’t immediately clear where she was teaching at the time of her arrest.

At Giannini’s second appearance in Superior Court on Thursday, Judge Richard Dubois granted public defender Eric Hove’s motion to continue to obtain and review police reports related to the case. Giannini, who is being held on $1.75 million bail, is slated to return to court on Nov. 5 to enter a plea and set a date for a preliminary hearing.