Armadale Detectives have charged a 32-year-old woman who allegedly broke into an 80-year-old woman's home on Tuesday and defecated on her front porch.

It will be alleged at around 1:15pm, the 80-year-old woman returned home to find the 32-year-old female inside her house, stealing household items and defecating on her porch.

Court.

The victim asked the woman to leave and it will be further alleged the woman grabbed the victim's arm demanding money. The woman fled the house after a short scuffle.

A short time later police will allege the same woman entered a fast food outlet on Albany Highway in Kelmscott and tore a necklace from the throat of a 16-year-old boy before trying to run away.

Staff and customers restrained the woman until police arrived.

The 32-year-old woman from Huntingdale has been charged with aggravated robbery, aggravated home burglary and commit an offence and stealing.

She is due to appear before the Armadale Magistrates Court on Wednesday.