Interesting theory.
Iirc, during the original whitewash H email crap fest, Comey confronted Lynch about an email he was given, where Lynch said (put in writing) that Hillary would not be prosecuted, period. Something about, her response: stoney silence.
It could be a simple as that, as well. That the email was true. That Lynch herself put the kibash. (Via O, of course).
Yeah, found it: