The script describes her as an 'old woman'.
EXT. NIIMA OUTPOST - CLEANING TABLE - DAY
TIGHT ON REY'S HANDS as she SCRUBS CLEAN her day's salvage. Rey
glances up: she looks at an old woman, also cleaning some salvage.
Rey watches her, gets lost in the simple moment. A small, passing
alien UNDERLING barks something to her in another language. She
returns to work.
She doesn't appear to be anyone special, just an elderly scavenger (to hammer home where Rey's life is heading if she doesn't embrace her destiny).
As to why Rey was looking thoughtful, this was actually because she was observing a mother and her child in the original cut. The shot didn't make it into the theatrical version of the film (although her reaction-shot did) but you can see the scene in its entirety in the official novelisation.
Glancing up from her work, her gaze happened to fall outside the tent.
The biped whose movements had caught her eye was human. A woman, clad
in wrappings of deep maroon that shaded to purple, a band of turquoise
makeup across her eyes and forefingers indicating her clan. Standing
on a ship’s open ramp, she surveyed her surroundings. A moment later a
similarly clad and decorated boy appeared and moved to join her. A
domestic exchange ensued, during which the adult did something to the
child’s hair. Returning to her work, Rey was only partially aware that
the brush she was using on a narrow piece of salvaged electronics had
begun to imitate the same caressing, grooming movement of the woman’s
Coming up beside her, one of Unkar Plutt’s assistants barked
at her and gestured in her direction with his staff, implying it would
be in her best interests to focus on her work and not allow herself to
be distracted. Without another glance in the direction of the mother
and child, Rey returned to her own work.
The Force Awakens: Official Novelisation