Sharn completely deserved to lose that final vote. When your livelihood is arguing as a barrister, you'd better showcase that advantage when you're in your element and making a pitch for jury votes and she underwhelmed in that capacity. I do think she would have bested Brian had she brought him but the main liability with him not being there is that made the focus of the entire final tribal council her gameplay and by allowing Shane AND the jury to frame that tribal entirely around the loyalty dynamic that was effectively the one area that Shane had her beat in, she ultimately sunk herself.
Episode 17 was a complete and utter disaster for Sharn's game in every respect. I said as much right after it aired. But her inability to frame those events with the jury in the way they ultimately went down - her effectively being goaded into playing her not-so-hidden immunity idol by Benji and then being used by him to effectively sink Mat's game - and trying to play those events off as loyal gameplay (when they were the furthest thing from it) - was her undoing. That day was her kryptonite and it was frankly a miracle that she was able to recover and game her way to the end against steep odds. That she didn't have a gameplan on how to best approach those events and seemed intent on brushing those aside and hoping they wouldn't come back up likely cost her the game.