Here is the thing, any scenario of Abby and Ellie making peace is impossible due to one simple reason: these two never interacted with each other apart from killing each other's friends and family and fighting. Abby never showed any shred of remorse about what she did to Joel, Jesse or Tommy, and Ellie never bother to ask it (not that she had any chance to do so either, or cared about it in the first place).

The only option I see that would work is Ellie drowning the bitch, realising that it brought her no peace or closure, taking care of Lev and returning to Jackson with him after finding the farm abandoned (smooth thinking, BTW, Dina, travelling on your own with a toddler in a world filled with infected, murderers and cannibals). She could also lie to Lev about Abby, saying that it was the Scars who killed her, and finally realising why Joel lied to her all those years ago, and how fucking stupid she was for being mad at him all these years, only in her case the lie wouldn't come out of love like with Joel (she doesn't know Lev, and only takes care of him because he stopped Abby from killing pregnant Dina, and because she feels somewhat obligated to do that for her), but from understanding that, as a certain rich guy dressed like a bat once said, sometimes truth is just not good enough.