Immacula Eugene, 51, and Marie-Margaret Petime, 46, were each arraigned near Montreal on Tuesday on two charges of drug trafficking, two of conspiracy and two of administering a noxious substance.
Eugene was also charged with armed assault.
The alleged crimes took place last July. The 87-year-old victim died two months later but it was only on Nov. 21 that police received a complaint from someone close to her.
Longueuil police spokesman Mark David said it is unclear whether the woman died directly from the alleged assault. The investigation is continuing.
Police arrested the women on Monday after reviewing video from within the centre.