What most of this comes down to is verbs vs nouns and adjectives. Adjectives and nouns take on endings that indicate gender and plural, while verbs are gender neutral. Therefore:

Io sono italiana (spoken by a female)
Mia socia (about a female, spoken by either a male or female)

Di chè cosa state parlando uses the plural form of stare, so it's "what are y'all talking about", but it would more commonly be said "di cosa parla/parli (formal/informal). The chè is routinely omitted, and the "stare+gerund" format is rather rare.

Similarly, while "sto andando ucciderla" is "I'm going to kill her", more commonly it would be said "I will kill her", "la ucciderò"

Hope that helps, I'm here anytime :)