。
She is one of the most distinguished painters of our time.
Literal
She [topic-は] modern-era [of-の] most outstanding painter [of-の] one is.
Three distinctly literary touches make this sentence feel like an art-essay or biographical entry rather than spoken praise. 最も is the formal superlative adverb 'most,' more bookish than the everyday 一番. 優れた is the past-attributive form of 優れる ('to be excellent, surpass'), used here to modify 画家 — Japanese routinely uses past forms to express a current resulting state. ~の一人 ('one of') is the standard frame for 'one of the [superlative] [plural noun]' constructions, a syntactic mirror of English. Closing with である instead of だ is the unmistakable signal of essay register: factual, distanced, written.