The statement conveys a sense of self-awareness and a deep understanding of one's identity and place in the world.
"She understood who she was" highlights the person's awareness of their own personality, values, strengths, and weaknesses. This self-awareness enables them to have a clear sense of their identity and purpose.
"Whose she was" suggests that the person also recognizes their place within their family, community, or cultural context. They understand their roots, heritage, and the impact of their background on their identity.