Cowan, a contestant on the show in 2004, denies assaulting the party-goer during an overnight stay at a lodge park in Lochgoilhead, Argyll, in December 2011.
The alleged victim, 36, told the High Court in Glasgow that she went to sleep in a room at his lodge after she thought she had been locked out of her own accommodation.
The woman said she woke to find Cowan, 39, from Glasgow, leaning over her. The woman said she had not met Cowan before the night out, where he was a guest of a colleague.
The witness said she drank around four gin and tonics, champagne and Red Bull before dinner, when she had a further four or five gins.
The trial continues.