Maybe you cant convince her you have told her hwta happened so let her deal withit, do not accept text messages form him ignore any overtures he makes , did your sister say why she wouldnt deal with it ? Is there a Dad around that can speak to him as thissmay be the way to go if he is pestering you, ask for family help first ...
yes, she said she directly that she did not want to deal with it. last time this happened my parents actually talked to the dad and as a result the dad cut off all contact between my nephew and my parents. there just seems to be something strange happenig under the roof of my nephew's house. his sister, my niece, suffers from anxiety and is to the point where he is pulling her own hair out- literally.
do you know what he really wants? you should talk with your nephew about what he wishes. you should offer him a private talk to find out, ask him what he likes about feet and pantyhose.