It happened shortly before 8:45 a.m. on the westbound platform at the Girard Station.
SEPTA released video of the incident on Friday afternoon, saying the circumstances are not yet known.
Shocking video shows woman fall onto Market-Frankford Line tracks as bystander comes to the rescue
The video shows the woman walking along the platform when she makes a turn toward the tracks and then suddenly falls over the edge.
She picks herself up and reaches the edge of the platform, but appears to have trouble pulling herself back up.
That's when the bystander comes to her aid, helping pull her up off the tracks.
It's not yet known if the woman was injured.
"SEPTA would like to remind riders to always keep safety top of mind and always stay behind the yellow line until the train has fully entered the station and has come to a complete stop," the transit agency said in a statement.