If I said "cozinho," the "I" is implied. What is the meaning of "ela cozinha" and other such examples specifically; is that formal, just extra emphasis on "she," redundant, or something else? What is the natural way to say "she cooks rice?" Or is it based upon context whether or not to use "ela?"
Normally, you would say Ela cozinha arroz, because "cozinha" can also be the kitchen. But when is implied that you are talking about a person, you can say just "cozinha".(mostly in answers) For example: Ela/ele cozinha? (Does she/he cook?) Cozinha. (She/he does).
In this case, it is clear that you are talking about someone instead of the kitchen.