My girl violated her probation by not changing address it is her first time violating probation what is the worst they can give her

She will have to attend a probation violation hearing. At that hearing it will be up to the Judge to decide if he wants to continue her probation, put her in jail for a few days, or revert back to her original jail time and make her do that. More than likely it will be more probation time with a stern talking to about reporting properly to the PO.

The worst that can happen, she can be made to serve her remaining probation time in jail.

Now that is not likely to happen but you did say what is the worst that "could" happen