Cowan, a contestant on the reality show in 2004, denies performing a sex act on 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, 36, from Glasgow, on top of her.
She said: "He was leaning over me and I started to fight him to get him off."
The trial continues.