the DOJ does not need a Grand Jury to indict
(although they might hide behind that process to excuse themselves when they do not indict)
I believe what you are saying is they do not have to indict with a Grand Jury to INITIATE criminal proceedings. That is correct. They could commence with a Criminal Information.
But they won't do that as they do not want to prosecute her. Rather, they go before a friendly Grand Jury, submit the evidence in such a manner as to assure no True Bill, ergo no Indictment, and all criminals (DOJ and HRC) come out smelling like roses.