The former Indiana teacher charged with sexually abusing multiple underage children while they wore "Scream" masks is setting the stage for claiming she wasn't in her right mind when she allegedly committed the acts.

Brittany Fortinberry's lawyer, Stephen Gray, filed a notice with the court to hire several mental health professionals to give his client a psychiatric evaluation.

Gray says he wants to see if Fortinberry suffers from a mental disease or defect, which "prevented her from appreciating the wrongfulness of the conduct the time of the offense."

After receiving the notice, the judge in the case has now signed off on an order for Fortinberry to get the psych exam ... this after authorities accused her of engaging in "gangbangs" with the students, among other twisted things.

Remember ... Fortinberry is facing a smorgasbord of felony charges -- 29 in all -- for child molestation, contributing to the delinquency of a minor, dissemination of matter harmful to minors, and more. She faces decades behind bars if convicted.

Police claim Fortinberry had a very specific sexual scenario she asked the children to act out using replicas of the killers' masks from the "Scream" movie franchise.

Cops say witnesses have accused Fortinberry of giving some of the alleged victims hundreds of dollars' worth of clothes before taking them back to her house to have sex.