Argentine national Marcia Celeste Fernandez Babio, 24, worked as an assistant to Gabriela Elena Spanic Utrera and over at least four months she administered to her and her family ammonium sulphate in both food and drink, the office said in a statement Monday.
Fernandez was arrested Aug 19 when she returned from a trip to Argentina.
Gabriela told authorities that she hired Fernandez as a personal assistant in January and the woman moved into her house.
However, since April, Gabriela, her mother, son and the boy's nanny began to have "health problems like vertigo, vomiting, headaches and abdominal pains, shivering and generalised weakness", the DA's office said.
At the beginning of August, the accused asked Gabriela for permission to go to Argentina to visit her family, and she subsequently left the country.
Gabriela, her family members and the nanny continued experiencing health "problems" and went to a doctor, who - after performing various tests on them - concluded that there was a high level of ammonium in their blood caused by poisoning which, over the long term, could have proved fatal.
The actress "noticed that the only person who was not sick in the household was Fernandez Babio ... (and) recalled that for some time the suspect had not eaten or drunk anything in the home, and when they had asked her why she had responded that she had already eaten", according to the statement.
Gabriela and her mother filed a complaint for attempted murder, which in turn allowed authorities to search the house, where they found two ampoules containing ammonium sulphate in Fernandez's bedroom.
In addition, when the woman was arrested, police found two more ampoules of the same toxic substance in her handbag.
Gabriela has acted in several soap operas, including "Decisiones", "Tierra de pasiones", "La venganza" and "La intrusa".