Board Thread:Spoilers!/@comment-25361971-20150928100931/@comment-26116863-20151001003722

Look, this wiki confirms it:

"It comes winding down toward Regina, and the group realizes the Darkness has chosen its new host. Knowing how hard Regina has worked for her happiness, Emma refuses to let this happen to her friend and takes up the Dark One's dagger."-http://onceuponatime.wikia.com/wiki/Operation_Mongoose_Part_2