Just think about how Snow acted when she realized that Gepetto put Pinnochio through and she could have been with Emma. (which I still think was wrong of her to slap him, it is ALWAYS about the CHARMINGS)
I think Snow was justified in slapping Gepetto. Emma grew up alone because of him, yes he had his reasons for doing what he did, but still Emma could have grown up with at least one parent. Snow’s immediate “I forgive you” felt forced in my opinion, I think Snow should have been angry at Gepetto a little bit longer then forgiven him.