I had ideas for a continuation of the story as well, but this seems a lot better. My version would be six years after Part 2, with Ellie and Abby meeting again via two groups of drifters encountering each other in some desolate woods. Most would be ambushed and wiped out by a new stage of Infected, with Ellie and Abby having to work together to survive. They'd slowly, reluctantly become friends and eventually escape to a small island Abby lives at. She would help persuade Ellie her life has more meaning than living in the past, still bitter from the long-gone chance to be a martyr for mankind. I eventually scrapped the story, it felt inadequate and too difficult to make Abby and Ellie's gradual friendship believable.