Astou is very nice to everyone she meets. She is person I know.

The sentence compares Astou with everyone the speaker knows, so it needs the superlative form of “kind.” Use “the” before a superlative adjective: “She is the kindest person I know.” “Kinder” compares two people, while “kindest” without “the” is not the correct form here.

AI-written and checked against the verified answer.