nifterah – she died
nifteres – a deceased female
When you say she was nifteres, you are actually saying she was/became a deceased female person.
The word niftar applies both the jmeaning , he died, and a deceased male. In nekaiva, there are two separate words for these things.
I always wondered about the expression “bigdei Esav, b’nah hagadol, hachamudos” (Breishis (Toldos) Perek 27, Passuk 15). Beged is loshon zochor, and chamudos, which refers apparently to the clothing, is loshon nekaiva. If anyone has an explanation, or if chamudos refers to some esoteric idea that is being hinted at, I would love to hear about it.
I have a similar question on the dikduk of
” kol melacha lo yay-aseh bohem.” (Semos (Parshas Bo Perek 12, Passuk 16). Melacha is loshon nekaiva, and yay-aseh (not ya-aseh)which means “it will not be done,” is loshon zochor.
My Rov did not have an answer for me about this.