The woman in the car at the service station in Chapter 29 is described very briefly, but specifically: "Her hair is gray but she has Orphan Annie eyes, wide, no lashes; she looks as if she has never blinked in her life" (29.51) The woman stares at Adam. She sticks her head out the window and eventually gets out of the car. And that's all we know about her.
We aren't sure what to make of his woman. She doesn't seem to reappear in Chapter 31, when we reencounter in the hospital all the people Adam met on his journey. But we wonder, is this some second incarnation of Edna, of Arnold and Edna? Both the service station attendant and Arnold use the phrase "You all right?" (29.52) to speak to Adam. If, as we suggested, Arnold was Dr. Dupont and Edna was a patient, this could be the same situation. After all, the service station attendant is tending to the woman in the car (as a doctor would a patient).