The 30-year-old British runner dropped out of Friday's 10,000m with nine of the 25 laps left to go.
She also pulled up in the Sunday's marathon, leaving the race about four miles before the finish line.
"I felt better within myself tonight but my legs just haven't recovered from the marathon. There just wasn't anything in them," she told the BBC.
Paula had been agonising about whether to enter the race after her disappointment in the marathon.
The 10,000m title eventually went to Xing Huina of China.
She sprinted away with 100 metres to go, finishing in 30m 24 secs.
The silver medal went to Ethiopian Ejegayehu Dibaba, with Derartu Tulu, also of Ethiopia, taking bronze.
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