I agree that by releasing Henry Regina took a big first step on what might become a path to redemption. But I expect it will be a long and difficult path, with many opportunities for backsliding, as we saw in her decision not to burn the book. I thought it was very telling that when she tried to return the spell book to Rumple she said we would never use magic again because she liked it too much. Apparently, magic is like an addictive drug.
In addition to her scenes with Cora, I thought the scene in which she brought Henry home revealed a lot about Regina. Even at the beginning when she had him in the tree and said,”Don’t fight it, honey. You might get a splinter.”, we could hear in her voice a conflict between her desire to use magic to control her son and her realization that she was hurting him. And of course, it was a reminder of when her mother used the tree branches to imprison her as well.
Then, her whole conversation with Henry seemed to be building to the moment when he said “I don’t want to be you”, echoing Regina’s statement to Cora. I think that was the moment Regina realized she had to let Henry go or she would just drive him away from her like Cora drove her away.
Of course, her decision to release Henry doesn’t mean she has automatically redeemed herself. She had almost no choice, but it is still a big step forward for Regina to put Henry’s needs ahead of her own and realize that keeping him prisoner would not “be what’s best for him” (as she so often rationalized in the past) but would have the same effect on him that her mother’s actions had on her. Now, the question is how far will she go in trying to earn Henry’s forgiveness and how tempted will she be to stick to her evil ways? I think the drug addiction analogy is a good one and she will start trying to do good but will often weaken.