Q:

Feminine case 3rd-person version of “Veni, vidi, vici”

How does the famous saying:

Veni, vidi, vici. 

have to be changed so that it describes a female person, such as in English:

She came, she saw, she conquered. 

Reversing Google Translate gives conflicting results. 

A:

"Veni vidi vici" means "I came, I saw, I conquered." 
"Venit vidit vicit" means "He/she/it came, he/she/it saw, he/she/it conquered."  It doesn't make any judgement about gender. 
If you think that the gender is important, Latin uses a demonstrative-y/pronoun-like particle: "is/ea/id" which correspond to "he/she/it" in English.  In Latin, one doesn't need to reduplicate the subject of a list.  If you chose to put "ea" before every verb, you would be emphasizing that SHE (and not anybody other person) is the one doing the action.  The translation you're most likely after would be:
"Ea venit, vidit, vicit."  She came, saw, conquered. 

A:

It's:

Vēnit, vīdit, vīcit. 

whether the subject is masculine, feminine, or neuter.  Latin only has grammatical gender agreement between nouns and the adjectives that modify them.  Subject-verb agreement in Latin only involves grammatical person (I, you, he/she/it) and number (singular and plural).