I will not beg, but I will not be afraid to talk to my own sister.
Thatta girl! Go back to your own pre-nearly-JW days and try to be who you'd be with a wayward sister. I probably wouldn't even acknowledge that e-mail. My brother and I go for periods where we're peeved with each other and then eventually we just get tired of being mad at each other.
Isn't playing by the cult-personality's rules playing by the cult's rules? Were you both non-JW's for some time? I believe if it were me, I'd continue interacting as though she never sent that e-mail.
But I'm annoyed today so I may not be the voice of reason.