It was a repeat of the Lingfield Oaks Trial 1-2 as the 14-1 winner beat Architecture, ridden by Frankie Dettori for Hugo Palmer.
Harlequeen was third, with Turret Rocks in fourth place.
Earlier, the £1,000 purchase Mrs Danvers scooped a first prize of nearly £123,000 by winning the Super Sprint at Newbury.
Seventh Heaven, a daughter of prolific stallion Galileo, put behind her a below-par display at Epsom to give O'Brien his fifth success in the fillies' Classic.
However, his main hope - the Ribblesdale Stakes winner Even Song - was well-beaten despite being sent off the 4-5 favourite.
Mrs Danvers retained her unbeaten record when defeating 22 rivals at Newbury.
Jockey Luke Morris pushed the Jonathan Portman-trained filly to the front two furlongs out and the  9-2 joint-favourite won by one and a quarter lengths, with Stormy Clouds second and Clem Fandango third.

He said: "With significant Tory and UKIP power blocks in the next parliament, we will be the left-of-centre backbone of a Labour administration.
"Along with the SNP and Plaid Cymru, (we) will ensure that the next Labour government remains true to its values."
Dr McDonnell said that, while his party had always worked closely with Labour, the SDLP was not tied to any other party.
He said its MPs would be elected on their own manifesto.
"During the last Labour government, we were unwavering in opposition to the Iraq War," he said.
"Our MPs voted against the cut in the 10p tax rate. We refused to accept 42 day detention.
"These were all issues that Labour supported."
The SDLP leader added that his party would "categorically refuse" to support David Cameron and the Conservative Party.

The Fed is expected to keep borrowing costs on hold but its economic commentary will be closely scrutinised for hints about future moves.
In Japan, the benchmark Nikkei 225 index closed down 0.8% at 16,974.45.
Shares of Japanese consumer electronics firm Sharp slumped nearly 12% on reports a takeover deal may be delayed.
According to Reuters, Taiwan's Foxconn - also known as Hon Hai Precision - may postpone its $6bn (Â£4.2bn) purchase of Sharp after receiving "new material information" and is requesting more guidance on its latest quarterly performance.
In China, the Shanghai Composite index rose 0.2% to 2,870.43 while Hong Kong's Hang Seng index dropped 0.15% to 20,257.70.
In Australia, the S&P/ASX 200 index ended 0.15% higher at 5,119.03 even though falling iron ore prices dragged on mining shares.
South Korea's Kospi closed up 0.3% at 1,974.90, despite data showing the unemployment rate hit a five-year high.
The rate rose to 4.1% from 3.5% in February, which was higher than economist expectations, due to a contraction in the manufacturing and construction sectors.
However, analysts say most global investors are focusing on the outcome of the Fed's meeting.
"Another hike is sharply at odds with Fed concerns about increased uncertainty around global/China outlook and market turbulence tightening credit conditions," said Vishnu Varathan from Mizuho Bank.
He added that attention was focused on any hints the bank might make about the frequency of interest rate rises this year.
Seventh Heaven, ridden by Seamie Heffernan, sprang a surprise to win the Irish Oaks for trainer Aidan O'Brien.
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SDLP leader Alasdair McDonnell has said if Labour leader Ed Miliband becomes the next prime minister "it will be with our support, on our terms, that he takes power".
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Asia markets were mixed on Wednesday as investors waited for the outcome of the latest Federal Reserve meeting.