I have seen both used in an instance like this but I believe that "a" would work better than "the". Also, if I knew more about the situation then I maybe could understand their wording a little more but I will just go off of the sentence you gave me.
Sara has been the victim of identity theft too.
Sara is not the only one who has had her identity stolen so this would not work since "the" is implying that she been the victim of a specific person. It would work better if the sentence was "Sara has been the victim of an identity thief" since she was the specific victim of this specific person. She clearly has not since there is the word "too" at the end, meaning that she has not been the only victim of this crime.
Sara has been a victim of identity theft too.
This is more correct, or at least, more common from what I can tell. Since Sara is not the only person to have had their identity stolen the word "a" would imply that she has not been a specific victim.
Now, the area where they used "the" instead of "a" could be the reason for their wording because I do not know how other places tend to word their sentences.