Decoste is accused of going to residences for seniors, claiming to be a CLSC employee.
Once inside, police said she stole money from her victims.
She was arrested on Sept. 10 and faces charges of theft under $5,000. She is accused in at least six separate robberies.
Montreal police say Decoste used several variations on her name, including the name Marguerite Blais.
Police are looking for other people who may have been robbed in this way.
They're asking anyone with information to come forward.
Anyone with information is asked to call 514-280-2222.