Simmonds is a native of the U.S. state of Utah. She lives in Bountiful, Utah. She has four siblings; two older and two younger than she. At twelve months old, Simmonds lost her hearing due to an accidental medication overdose. Her mother learned American Sign Language and taught the family so they could communicate with her. When Simmonds was three years old, she started attending the Jean Massieu School of the Deaf, where she participated in its drama club. After completing sixth grade, she mainstreamed at the Mueller Park Junior High School in the fall of 2015. She has performed at the Utah Shakespeare Festival in Cedar City, Utah, and her sole film experience before Wonderstruck was a deaf student's short, "Color the World". Simmonds has a cochlear implant to help her hear.