The Warehouse mounted a cross-challenge to the authority's determination that her dismissal was unjustified.
In the Employment Court, Ms Harris claimed that The Warehouse's investigation against her wasn't fair and that evidence that assisted her was disregarded.
Her actions, she argued, didn't constitute serious misconduct.
The company claimed the authority erred in law in finding that Ms Harris' dismissal was unjustified because The Warehouse didn't consider it relevant that they had no previous performance concerns with her.
The Warehouse said that, having found her conduct serious, it justified dismissal; the presence or absence of any previous performance concerns wasn't relevant.
In its decision released this week the Employment Court found in Ms Harris' favour.
On the company's claim that Ms Harris's conduct brought it into disrepute, Chief Employment Court Judge Graham Colgan said: "In the circumstances of this case, it could not have been concluded that Ms Harris brought TWL into disrepute in a way that constituted serious misconduct simply because [the complainants] considered she had done so, or even because [store manager Richard] Bunce agreed with [their] assessment."
The judge recommended that, as a major retailer with a head office, The Warehouse consider more specialist support when dealing with complaints where a difficult investigation may well lead to dismissal and a challenge to it.
He upheld the authority's determination that Ms Harris was unjustifiable dismissed and ordered that she be reinstated.