I don’t think anyone realizes how much she really trusted Damon with. She trusted him with not only everything, but everyone. She trusted him fully and completely to the point where he got her to settle down at the boarding house and wait it out till the storm subsided. Elena put her complete and undying trust and faith in Damon and even though the plan failed, he never betrayed her trust. Everyone who was a part of that plan, everything that could have gone wrong with it, everyone who could have gotten killed; Elena trusted Damon with it. Damon has never failed her, even when she was attacked by Stefan, it wasn’t that he had failed her its just that he wasn’t there, and even then he returned and gathered her up in his arms to take her back home to where she was safe and would continue to be safe. Damon, no matter what; will always and forever know how to stand toe-to-toe with Elena, and will always protect her no matter the cost; and Elena knows this. She believes in him like no one ever has.