A volunteer diver from the Slidell Police Department discovered the car in Bayou St. John, with the help of Louisiana State Rep. Austin Badon, who together spearheaded the search along the waterway.
Monette, 26, disappeared after a night celebrating her nomination for a "Teacher of the Year" award at Woodland West Elementary, spending the evening with friends at Parlay's Dream Lounge in New Orleans.
Authorities said they focused the search along the waterways, which Monette would have had to drive across the bayou to get home.
Friends told police they last saw Monette at her car, and said she planned to sleep before driving home. A New Orleans traffic camera recorded her making a turn in New Orleans around 5:15 a.m. the next day.
"To know that she could have possibly been there for three months," said Toni Enclade, Monette's mother, "I'm in shock. I can't believe this. I just can't believe this."
A native of Long Beach, Calif., Monette graduated from California State University last year and moved to Louisiana to take part in the "teachNOLA" program, which places teachers in impoverished areas in the city.