How? Comey is not AG.
Now there's another red herring to waste time on.
Legally, the situation has not really changed. She's never going to prison. Ever. But it's the political situation that's changed.
If Comey played it by the book, he would have handed over the results of his investigation and walked away, leaving it with Lynch, Obama, the Clintons and the media to spin it.
Lynch has changed everything with this statement, again politically not legally.
Not bound by professionalism any longer, Comey is obligated now to say "indict" or "she didn't break any laws", and she absolutely undeniably broke laws regarding her handling of classified data.
Comey cannot maintain his professional reputation and respect in the intelligence community without publicly listing her crimes and recommending she be prosecuted for them. Politically that's a stake in the heart, regardless of the legal machinations down the road that keep her out of jail.