Well, that's a bit of a mystery. There are no definite clues about Sarah's whereabouts after the story. It could be that she's still in the area, or she might have moved on to a different place to escape the remnants of the chaos.
Well, there's no definite location given for Sarah after the story. It could be that she went off to start a new life somewhere, but that's just speculation.
Well, Sarah in the 'Days Gone' after story may be involved in establishing a more stable community. Given her intelligence and resourcefulness, she could be part of creating rules and systems that ensure the safety and growth of the group. For example, she might help set up a proper medical facility and train others in basic medical care. Also, she could be involved in diplomatic relations between different survivor groups, using her calm demeanor to defuse tensions and promote cooperation.
Yes, she is. Sarah has been important throughout the game, and in the after story, her skills and knowledge would still be highly valuable to the survivors.