Again, Rebecca was not the subject of a criminal investigation. She had made herself available to LE for interviews and questions, even as she spent most of her time ferrying Jonah & Dina's friends and relatives to and from the airport.
The investigation by CPS was a criminal investigation. iirc, RZ's phone call detail did list a call from a detective. And, of course, RZ would herself know whether she told LE the truth. Making oneself "available" is no guarantee one has told LE the truth. According to the records released, it was medical staff who alerted CPS that the injuries did not match with the version of events told by RZ.
JMO