The Title: Baroness is one of 3 unique and extra titles that Bounty Hunters can earn during their Class Storyline on Alderaan if they choose the right cutscene choices.
Unlike the other two, the Baroness Title can only be earned by Female Bounty Hunters that engage in the optional side-romance with Raffid Girard.

Upon arriving on Alderaan for your class story, choose the [Flirt] Options directed at you by Raffid, between missions you will constantly return to the Girard family, you must make sure to act nicely and support Raffid during these cutscenes regardless of the quests.

Towards the end of the Girard story on Alderaan, your character will be put on the spot to choose the successor to House Girard. You must pick Raffid during this cutscene.
As a reward for choosing him as a successor and prior chosen [Flirt] Options, he will ask you to become a Lady of House Girard.
If you accept the offer the next Quest reward will also reward you with the Title: Baroness.

Male characters and Female characters that chose Raffid as successor but did not [Flirt] (or those that Flirted but did not choose Raffid as successor), do not earn this extra title upon completion of the Alderaan storyline.

Likewise choosing dark options and killing every single member of all families you come across (as well as rejecting extra missions and aid from families) will reward your character the Title: Homewrecker.