Visitation rights??

Deb
My sons father and I have been broken up since I was 4 months pregnant and I have a final restraining order on him due to him threatening me and harassing me. Now his sister and I was on okay terms but now she seems to be getting super controlling of my son making it seem she trying to get visitation rights too see him on his behalf. 
She told me if I do not let her see her nephew she will fight for visitation rights. Can that even be possible???