I hope you really DO report anything you hear or see. I hate to sound like a broken record, but it is not up to you or the school to "investigate" or try to determine the veracity of the claims, you are just supposed to pick up a phone and make a call.
My daughter told her school nurse, school principal, school vice principal, two teachers, her guidance counselor and a PSYCHIATRIST that she had been molested daily for two years and all of them called me to "investigate" instead of reporting. I confirmed that I had just learned of it, and they asked if I wanted them to call and I said YES. I wanted there to be lots of witnesses to her revelation. It was not until we complained to police and charges were filed that I learned I was the ONLY person to report it. I even wrote to the medical board about the shrink and they wrote back to say they weren't getting involved.
I'm so sorry you and your daughter had to go through that nightmare. It was drilled into me to report any suspicions of abuse no questions asked. I have called before and it was dealt with properly.