You see? This chapter is exactly why you leave honorifics and certain Japanese terms untranslated. That whole bit in the middle with her demanding to have him say "sister" in three different ways make ZERO sense when translated to English. However it makes *perfect* sense if you leave the terms as nee-san, onee-chan, aneki, Athena-neesama, or whatever the original text was.
The Japanese culture and the Japanese language are nearly inextricable, and trying to map them to non-existent English equivalents is an exercise in frustration for the average manga reader and an exercise in futility for the translators.