I'd politely disagree. I do think she is still not over joel, but definitely had a massive epiphany at the end. After losing pretty much everyone around her weather through violence or choosing her own shitty interests over everyone elses, she finally realized that nothing she could do would fix anything. She had some kind of deathwish and hoped that Abby would have the ability to kill her. But since Abby was pretty much starved and left for dead she was in no shape to give Ellie the death she wanted and now it was too late. her only opportunity for any kind of redemption was to let her go or her having an emotional breakdown left her with no will so she let them go. Also the implications that Abby is actually going to make it to the fireflies really gave me the hope I was looking for in this game. Because if the fireflies are reforming then they are still looking for the cure and that the story really far from over.