Senior Parent - What could this be?

Hi Durham neighbours. I need help making sense of what just happened to my mom and what to do about it. She told me this story this morning and I was absolutely beside myself and feel scared to leave her alone now.

My mom is 68, retired, a tiny Asian lady and is home alone for most of the day. Yesterday midday she was shoveling our walkway when a car pulled up in front of the house. A lady from the passenger seat rolled the window down and asked her for water. My mom told her to wait and she was gonna grab some. When she got in the house she realized the lady had followed her and walked right into the house as well. My mom gave her two water bottles for her and her presumed husband (male in the driver's seat). The lady asked to use the washroom, which my mom pointed her to. After using the washroom the lady insisted on giving my mom a gold necklace, said it's their tradition and that she's very grateful and that my mom is a very good person. She insisted my mom put the necklace in her jewelry box. My mom doesn't have one, or have any nice jewelry at all. The lady even went into their bedroom and opened drawers trying to find something nice to put the necklace in, but my parents have nothing valuable in there, no cash, only documents. Eventually my mom came up with a cheap pouch and the lady let her put the necklace in there and then left.

Now I KNOW there are red flags all around and my mom absolutely heard it from me. I've heard of distraction theft especially among seniors but we haven't noticed anything stolen, nor is there really anything to steal. I'm really confused why she even left the necklace. My hunch is that they were scoping out the house and intend to come back and break in, and while there really isn't anything of value to take, of course I am scared for my mom's safety. My friends suggested I tell the police. Does anyone know of any other cases like this? What should I do at this point? Appreciate any help.