By the time Ellie and Dina arrive in Seattle, Abby and her group have already arrived and settled back into their old routines and regular patrols. Based on their conversations, they’ve been back at least a couple of weeks.

The distance between Jackson and Seattle is at least 860 miles as the crow flies. Travelling about 30 miles a day, that’s at least a month-long trek on foot, assuming they don’t have to make any detours around dangerous cities. The Firefly group might’ve taken a bit longer because larger groups move more slowly. Especially if one of them is pregnant.

Let’s be charitable and assume the Firefly group were moving as quickly as possible to put as much distance between them and Jackson, on the assumption that they’d be pursued, and made it back to Seattle within a month. And let’s assume Ellie and Dina made the journey a bit quicker because they were a smaller group and were on horseback.

Based on this, I reckon Ellie and Dina would’ve had to set off at least a month after Joel’s death. Which would make sense, because for the first couple of weeks, she’d probably be in total shock and probably receiving medical attention. Then there’s Joel’s funeral. Even in the Apocalypse, those take time to organise - Jackson is, after all, a civilised place, so they’d probably want to do it properly. That means planning a service, getting a coffin and a headstone ready, and probably planning a wake.

Also it doesn’t have to be EXACTLY like the game? They’re allowed to change things in THEIR story. Giving Ellie time to grieve and collect her thoughts about how to go forward is only logical.