Prior to her pilgrimage, Arin ran with a small group of other quarians around her age. Children of some of the Ilyas' crew members, mostly. They were known across the ship for being a bunch of trouble makers, though really, none of them did anything too terribly out of line.
When Arin returned from her pilgrimage, this had all changed. The teens had found a particular fascination in the geth, and the 12 of them each had a plan. They were going to steal command of the Ilyas and use it to jump back to the Veil to face the geth, somehow believing that they could reason with or befriend the machines before being destroyed. They let Arin in on the plan, fully believing that she would help them, something that should have been particularly easy considering she was the XO's daughter. They were wrong.
On the day the group was going to put their plan into motion, which was also the day Arin was supposed to be leaving the Ilyas to join her new ship in the fleet, Arin confronted them, trying to stop them from trying this foolish plan. The confrontation escalated much faster, and much more dangerously than she ever expected it would. Shots were fired, but Arin had much more experience with a gun than those fools. In the end, only one survived--a boy named Kiliev, the son of the captain, and her now ex-boyfriend, if that's what you wanted to call him. Her father had entered the deck, and all he could see was Kiliev on the ground, bleeding through his suit, and Arin standing over him with a gun to his unmasked helmet, blood all over her suit. It was her word against his, and his word claimed that Arin went insane.
Kiliev told everyone that Arin had come onto the deck and dropped words about how she wanted to erase that part of her life since she was leaving to a new ship, and that she didn't want any baggage, so she was going to kill the lot of them. When Arin tried to tell the truth, there was nothing to back her up. The kids had been smart and used a VI to erase any of the extranet searches about the geth and such, leaving it completely untraceable.
When the case made it to the admirals, the only evidence they had was 11 dead bodies on the deck, and the captain's son soon to be pulled off life support, whose dying words were a rather convincing "I thought she loved me,... why would she..."
Even Arin's father didn't stand up for her at the court hearing.
Within 48 hours of the whole thing, Arin was exiled--stripped of her name and any chance to become part of another ship. She was given the ship she herself had found on her pilgrimage, the Yaksha, and enough resources to last a few short months.
When she left, her father didn't even say a word to her. He just pulled his sobbing teenaged son away, back to the Ilyas.
He has been dead in her eyes ever since.
