Most quotes that go viral under a famous name are fabrications, misattributions, or drift from a different author. This one shows none of those markers. No rival originator has ever surfaced, no earlier printing under another name is known, and the sentiment matches her documented views so closely that a paraphrase of her memoir is the likeliest explanation.
The strongest candidate for what it paraphrases is a passage the aggregators reproduce without a chapter locator — everyone has to be different, you can’t copy anybody and end up with anything — ending in the one sentence Wikiquote pins to chapter 4 ↗ of Lady Sings the Blues: “No two people on earth are alike, and it’s got to be that way in music or it isn’t music.” Turn that into something you can fit on a poster and you get very close to the quote in question.
That remains an observation, not a finding. The 1956 memoir is still in copyright and its scans are lending-restricted, so it cannot be searched end to end from the open web — which is precisely why this page stops at “attributed” rather than declaring the line a paraphrase outright.