Nancy; I'm not sure what you are getting at.
In that context, yes. If she lit a fire, and the fire generated sufficient smoke, and someone searching for her saw the smoke, they might be likely to have connected the dots and gone to the rescue. Now that we agree on that, where do we go next?
You see, if you frame the question in that way and you say "assume she did light a fire", you are guessing. You are assuming. Nancy, she may have lit a fire. She may not have. We do not know exactly what she did. She may have had a fire going for 5 straight days, and then it went out. Maybe it was not burning when anyone was there to see it. Maybe she was foraging, or maybe she was already dead and being eaten by crabs. Maybe her and Fred were playing gin rummy. Who knows?
There's no end of possibilities. But to say that she would have had a fire and the fire would have been seen doesn't prove or disprove anything.