Cara Dune had a pivotal role as an elite shock trooper during the rebellion — and afterwards, when she and her small teams were tapped to continue destroying the remnants of the Empire. Then she became one of several "peacekeepers, escorting delegates, suppressing riots," a role that used to be occupied not only by Coruscant Guards but also by Jedi Knights themselves. Put together, she should be a vaunted member of the Republic. But Dune says only that she didn't sign up for these peacetime duties and took an early retirement.
The term "early retirement" is vague, so maybe Dune's initial concerns about rejoining the Republic come from some sort of AWOL status. But given her record and the high-level connections she would've made over the time of her service, that should be no big deal.
Sometimes a soldier will want to get away from the violence and heal in a peaceful corner. But it's obvious Cara Dune has no such desire. So why is she hiding out when we first meet her, and why was she so reluctant to rejoin the Republic?
Since she's not trying to stay out of battle, nor has she committed any egregious offenses against the Republic, the only logical reason for her reluctance has to be something dramatic in her past. A dark secret. Either a sin or a tragedy still haunts her, something even more personal than Alderaan.
