What should I do about old nieghbor using my Grandma for a commission?

I have cared for my Grandma for 8 years, and have POA over her. She is 91 with dementia and has just moved into a care home. Her old neighbor has visited twice under a false name trying to talk her into selling her home which is her income for the care home so she can take the commission. How can I stop this? restraining order? My mother is on my side but lives in another state. My grandma has a phone in her room and talks to the neighbor on the phone as well, and told her she can have it sold in 3 days, and will help her take my POA away so she can help her. I'm scared and very frustrated!!