Fade to Silence

Issa is a character that randomly appears in your camp, like Tua, Ryme, and Ezra. She did not appear in my first play-through because I think the max number of recruits you can have at your camp is 7 (there are 8 total). She was the last recruit I needed to complete the game 100%.

After starting a new game, I recruited the two event-based characters near the camp in order to get resources going. On your way to add these two members, it is wise to chop some trees and hunt some deer to add collection spots for your members. Once firewood & food was stored in reasonable amounts, I would rest for ~24hrs at a time in hut I built near the edge of the camp, run to the flats, turn around and come back. Rinse & repeat until there are action items for current members of the camp or a new person appears.

I would recommend turning away any other random survivors that appear in camp if you only need certain ones. Having more survivors is an unnecessary resource drain if you are using this rest method. With new people you DO want to recruit, I always responded as politely as possible for them to join.

UPDATE: all 8 survivors can spawn in one play through. You would just have to be patient and keep attempting to spawn them by returning to your base after some time has passed.