19-year-old Ayesha Muhammad of Philadelphia was charged with assault on Thursday. She was ordered to be held on $35,000 bail.
The alleged abuse happneed at the upscale Quadrangle community at Sunrise Senior Living at 3300 Darby Road in Haverford, Pa.
One of the workers, Samirah Traynham, was taken into custody late Monday night.
Authorities say the family suspected their loved one was being abused, so they set up a hidden camera - disguised as a clock - in her room.
In the video, authorities say you can see the care providers taunting and tugging at the ears of the 78-year-old victim. Moments before, the victim was topless and police allege Traynham struck the victim in the face and head.
"Traynham and the other employees are seen engaging in acts which I can only describe as humiliating, taunting and abusive in this case," said Delaware County D.A. Mike Green.
Traynham is charged with neglect and recklessly endangering another person.
Another woman, Tyrina Griffin, is also charged with aggravated assault.
"It was not intentional," Griffin said to Action News as she was led into the police station.
The Quadrangle is run by Sunrise Senior Living. A regional director spoke briefly on Wednesday afternoon.
"We are cooperating fully with police and all authorities," said Brent Russell. "We are certainly the people most eager to make sure justice is done."
The district attorney didn't rule out that others, including high level administration, could face charges.
RELATED: How to report elder abuse
In Pennsylvania, visit the website for the Department of Aging or call 1-800-490-8505
In New Jersey, visit the website for Adult Protective Services or call 1-877-582-6995
In Delaware, visit the website for Adult Protective Services or call 1-800-223-9074
For resources in other parts of the country, visit the website for The National Center on Elder Abuse.