The grandmother's ring - Detective Riddle

A woman calls up Detective Mehul to say that her grandmothers ring had been stolen. When Mehul visits her house, he sees broken glass on the lawn and dirty footprints. he arrests the woman. Why?

If someone had broken into the house, they would have left broken glass inside the house - the window was broken from the inside. If someone had broken into the house, they would have left broken glass inside the house - the window was broken from the inside.