Personally I believe(and hope) its a new character. It would be interesting to have a playable female lead opposite of Chief in some way.
Another theory is its actually Cortana or some type of AI in Spartan armor which would make it a full robot I guess. I’m not sure if there are actual robots in the Halo universe. Like Human versions of Forerunner Sentinels.
Who do you think is in the new armor? Notice it has an ONI symbol on the chest.