Violation of the right to privacy

Dear PAO,

My friend is dating someone who keeps demanding her to send him nude photos of herself through a messaging "app." My friend feels that their relationship is already very toxic because of his incessant demands. She has already deleted his messages on her end and then she asked him to erase their conversations on his end, especially the nude photos she was forced to send, but he did not do as told. My friend decided to virtually access his account through the "app" since he gave her his username and password. My friend took screenshots of their conversations and saved those files for her security, in case he will make things up about her or in case she needs to file a case against him in the future. But he told my friend that she violated his constitutional right to privacy and that she cannot use their conversations as proof against him. What is this right and did my friend really violate it?