When a person is arrested for a felony, they have the right to be arraigned, which means charges are filed and they have the right to enter a plea to start court proceedings. If the charges aren't filed, they are supposed to be released, this must take place within the 72 hours.
In her case, my guess would be she was arrested and the case was taken to the DA's office, who felt there was not sufficient evidence to file charges and asked the Police/Sheriff to do additional follow up. The follow up is being completed and, at the same time, they want to keep her in custody for whatever reason, flight risk, etc.
With the knowledge she was going to be released at the end of the first 72 hours, the officer made a call to the jail or went there, as she was going to be released and arrested her again, starting the 72 hour clock over.
The case will be presented to the DA's office again and charges are likely to be filed within the next 72 hours. I have rarely seen it go past the second 72 hour period, because the court tends to frown on that.
Please know there is a difference between probable cause to arrest and sufficient evidence to file charges.
You can PM me if you like....