Not saying Nephthys is free of guilt in it, but... even though she could have easily backed her argument by bringing up Seth's role in causing kid Anubis' suicide, she spared Seth that one very sordid detail that she knows (because her "lobotimized" version had found it out) and which Seth is still pretty much unaware of: how his mistreatment of kid Anubis had caused kid Anubis to even commit suicide once, due to Seth's horrible mistreatment of him (it was revealed at the end of chapter 18, described in more detail in chapter 19, and shown in a flashback within flashback mid chapter 60).
Not saying Nephthys is free of guilt in it, but... even though she could have easily backed her argument by bringing up Seth's role in causing kid Anubis' suicide, she spared Seth that one very sordid detail that she knows (because her "lobotimized" version had found it out) and which Seth is still pretty much unaware of: how his mistreatment of kid Anubis had caused kid Anubis to even commit suicide once, due to Seth's horrible mistreatment of him (it was revealed at the end of chapter 18, described in more detail in chapter 19, and shown in a flashback within flashback mid chapter 60).