。
She says she's the kindest woman in the world.
Literal
She [topic-は] this world-in [most-最も] kind woman is [quotative-と] says.
A self-claimed superlative: 世の中で ('in the world') sets the comparison frame, 最も ('most') marks the superlative, and the と言う ('says') framing reports her own self-assessment rather than the speaker's judgment. The choice of 女 (rather than the more polite 女性) is mildly noteworthy — 女 alone can sound blunt or even slightly self-deprecating depending on context, and here it adds a tonal flavor of either casual self-description or perhaps brashness, depending on how the listener takes it. The framing と言う keeps the speaker neutral about whether the claim is justified — she's just reporting what was said.