Treason
When Tali told Shepard about the admiralty board accusing her of treason, Shepard thought they were crazy. There was no way in hell Tali would ever do such a thing. She was too innocent, too kind and cared about her people too much to just betray them. In a heartbeat, Shepard agreed to go to Tali's trial and speak for her.
Once the trial was over, and Tali's charges had been cleared she could forget anything had ever happened. It was a tragedy that Tali's father had died but she would mourn him and move on, knowing that when the day came the quarians claimed their homeworld back, he'd be smiling down on her.
Shepard on the other hand was glad she was able to resolve the problem. Tali was like a little sister to her. They had a lot in common – being raised on ships was one thing. She would do anything to make sure Tali could stay apart of the Migrant Fleet.
And that's exactly what she did. Yell at the admirals long enough until they realized Shepard was right.