ESA was introduced in October 2008 when James Purnell was in charge at DWP, for new claims only; the numbers claiming ESA were quite low and excluded long-term IB claimants who made up the bulk of sickness benefit claimants at the time.
Cooper was the Chief Secretary of the Treasury at the time, and happily waved through the money for the "reforms".
Cooper introduced ESA for IB claimants, 1.5 Million of them, despite being aware by then of the inherent unfairness of the test and despite the concerns of GPs, disability groups/charities; she is responsible for the national roll-out of ESA for all claimants.
The review did not address the test, change the parameters of the test, or make any positive changes to the test; what it did was suggest improvements to the way claimants were supported into work. Cooper is on the record as saying that ESA claimants, irrespective of what their illness or functional disability might be, should be expected to move into work after 2 years on benefits - and she expected to see the majority of long-term IB claimants subjected to the WCA put on to JSA.
Cooper also changed the Access to Work funding, putting more responsibility on employers to pay for adjustments; without addressing discrimination in the workplace, this had the effect of putting fewer people with health problems into work. The various schemes she wanted to implement did not happen as Labour lost office, but none of them did anything to address the WCA itself.
Cooper also brought in a much tougher regime for WRAG claimants - what was supposed to be "personalised support" from an adviser was in reality nothing more than an opportunity to impose conditions on the claimants, subject to sanctions.
She may not have introduced ESA for the original tranche of new claimants - but she brought it in for the majority of claimants even though it was known by then that the WCA was not fit for purpose, and the few changes she made to ESA rules made matters worse.
The article you link to does not actually suggest that the review was positive. Cooper said this - as quoted in the article - "This is a 'something for something' approach which gives people more help alongside a responsibility to take it up so that no-one who is fit for work is left to a life on benefits". The difficulty being that many of the people tested were not actually fit for work, and the roll-out to IB claimants she is responsible for has blighted the lives of many people, forcing them into jobsearch conditionality they simply cannot comply with.