Sarah Fellows said she had been "absolutely devastated" when she was informed by a senior nurse about the incident three days after it happened.
The Trust is currently at the centre of a public inquiry into serious failings of care between January 2005 and March 2009.
Between 400 and 1,200 more people died than would have been expected between 2005 and 2008.
An independent inquiry into events at the trust in February 2010 found it had "routinely neglected patients".
The Trust has paid out more than £1 million in compensation to 120 victims of abuse, or their families.
An £11 million review of what went wrong at Stafford Hospital will be published on February 6.