Jannira Walker, 21, was arrested Saturday. She is facing charges of robbery, theft and related offenses.
Police say she, like the other two suspects, may be homeless.
Joaquin Rivera, a community leader, musician, and educator, died in the emergency room at Aria Health's Frankford campus the night of Saturday, November 28th.
Video cameras caught the images of Rivera being robbed as he died.
Police had previously arrested Martin Smith, 41, and Richard Alten, 44. Both are facing the same charges as Walker.
Investigators said the trio stole watch from Rivera's pocket, which has since been recovered.
As of this weekend, Aria Health had declined to comment on the Rivera case as a number of investigations go forth, including a probe by the Pennsylvania Department of Health.