That witnesses testimony could be quite off-topic, or extremely relevant, depending on what happened. She might have been a victim closest in age to him, showing his early disregard for consent... but that sounds more incriminating for a rape charge. On the other hand, if they were not close in age, or if he expressed verbally his sexual interest in Girl children and babies, it would be very on topic. If her testimony would be helpful:
1) she could be subpoenaed, willing or not . But who wants to torture an unwilling witness who would give the most unhelpful version of the truth, at best, if forced to testify. The prosecution looks mean and gets little information, if the witness does not lie, and no info or exculpatory testimony if she does like.
2) It could be arranged to have the witness interviewed by a forensic psychologist with her appearance pixilized and voice disguised. Then the psychologist could testify. This would be an option if the witness wanted the jury to know what happened, but wanted her ID protected from those who don’t already run in those circles, and know. It seems to me that she would be shamed and blamed - IMO - based on what I know of this circle of independent Baptist’s.