When asked if she thought the exorcisms could be making people with mental illness worse, Brynne disagreed.
"We do this under Dad's supervision. We never do it alone," she said. "He's been doing it for 30 years. He would know if something was going wrong."
However, Bob Larson has been accused of fraud and taking advantage of vulnerable people who are either desperate or prone to suggestion.
The Rev. Darrell Motal of the "Soul & Spirit" Para Church, who believes in the existence of demons, told "Nightline" that Larson is too quick to blame someone's problems on demonic possession and that it's more likely that Larson's clients need mental health care and spiritual guidance.
Father Edward Beck, a Roman Catholic priest, echoed Motal's comments and said he also believes that these young girls are "unqualified" and "unprepared" to perform exorcisms, and that it could be dangerous for them, as well as their clients.
While Larson admitted that he was not a mental health expert, he said if a demon is "blocking the therapeutic help, the therapy's not going to go anywhere significantly."
"Get the demon out, the impediment, and then the therapy can go forward," Larson said.
What's more, Larson and the girls' exorcism sessions are not free, and he insists that one session almost never does the trick.
"We have to fund what we do," he said.
Larson is currently weighing several offers for new reality shows starring Brynne, Tess and Savannah.