You can't validate the invalid. You know you weren't deleting messages or hiding anything so don't give that accusation too much of your energy. The more you try to defend yourself, the more guilty you will look, and things will heat up all over again. It's a trap - don't fall into it! Don't take the bait!
Stay calm and continue as you have, validating her feelings.
Give her space and time to regulate her emotions. And try not to get too frustrated while you're waiting for that to happen. She'll come around... .eventually.
Sorry I can't give better advice. I know it's stressful and frustrating. I've done a lot of waiting myself for him to get over crazy notions he dreams up in his own head. Nothing more I can do but validate... .and be patient. And in the meantime, finding some pleasant distraction for myself. I can tell you that over time, his fears have lessened and his accusations have gotten a lot less ridiculous. But I still have to ride the waves as they come.
Helps to remember our job isn't to change their moods or convince them of anything, but to protect ourselves from the fallouts and keep things from escalating.