The former lover of Seven West Media boss Tim Worner has been ordered to foot the company's legal bill after the Supreme Court found she made allegations she "could not substantiate" and acted unreasonably in her legal battle with the media company.

Amber Harrison, a former executive assistant at Seven, has been at the centre of an ugly court battle with the company since she went public in December last year with embarrassing details of her 18-month affair with Mr Worner.

In a judgment delivered on Monday, Justice John Sackar said Ms Harrison's conduct had been "unreasonable" and it was "necessary and appropriate" to order her to pay Seven's costs on an indemnity basis, which is higher than the costs typically awarded in legal disputes and would cover its entire bill.

The costs are likely to be in the order of hundreds of thousands of dollars.