By law in South Carolina, a report of need on potential abuse must be taken by the Adult Protective Services Dept, and an investigation must take place if the person is at imminent risk of danger and is vulnerable. It is the "vulnerable" part of that law that is causing the problem here.
The Omnibus law about adult protective services in SC is very specific about mental capacity; if the person is able to function and make choices, they themselves must make a report of abuse. Minor mental impairment is often not enough. And as a result, Adult Protective Services will not investigate (called a no need) if the person is capable of initiating a report.
However, that does not mean that you cannot encourage the person to make a report themselves (to the police as this possible sexual abuse) or that you cannot write a letter of concern to local law enforcement. Or that you call Adult Protective Services at the SC state level and implore them that this woman is more mentally impaired that she might seem.
The contact at SC is:
Mildred S. Washington, LBSW
Director of Adult Services
Department of Social Services
P.O. Box 1520
I know that you would like to hear better than this and that there is a way to get definitive action. But, SC adult protective services ties the hands of many reporters, and I too wish this was better. I work with protective services in another state and SC has a comparatively weak policy that allows these type of system cracks to develop.
Encourage your friend to self report. Ask that she goes to a women's shelter or to the police (I know she is probably very hesitant)...But, soft words over time can break hard bones, as Solomon said, and this is, your friendship, probably the best way to get her to take action on this abuse. I share your frustration on this issue as well. Steven