A: This sounds like a tense and delicate situation, as family conflicts involving aging parents often are. Ideally you would be able to reason with your sister. It’s understandable that she might become defensive in this scenario, but hopefully she can get past that and understand that your concerns come out of love – that you’re not just trying to give her a hard time. Mediation can often be helpful in situations where there is conflict between siblings involving an aging parent’s care, even in its just informal mediation. Consider engaging another family member or close friend that you both talk to, another sibling perhaps, to talk to your sister on your behalf and reopen paths of communication so that you can assure that your mother isn’t being neglected and is not living in an unsafe environment. Maybe another family member in the area could even visit them at home and help allay some of your concerns.
If your sister can’t be reasoned with and alternatives aren’t working out, the agency that you would contact is Adult Protective Services. Adult Protect Services “are the first responders to reports of abuse, neglect, and exploitation of vulnerable adults.” They have the mission and the mandate to investigate your concerns and determine whether your mother is being properly cared for. You said that your sister has only been responsive when you mention involving authorities, so this action may be one that helps turn the situation around.
If you do ultimately need to contact Adult Protective Services, you can locate the appropriate office at the National Adult Protective Services Association website. Adult Protective Services generally approach situations like this with the goal of making a positive difference for everyone involved, so I would expect them to work to find a good outcome for your entire family, your sister included, rather than making your sister out to be some kind of villain. Their basic protocol in scenario like this would be to evaluate the situation and your mother’s well-being, and if necessary, put in place a case-plan and monitor the situation on an ongoing basis.