Elthara random events at her spot in the Wayfort where she's caught in the heat of action with certain non-party companions and/or denizens of the Wayfort.
The only issue I would have (and that means it's just my opinion), not that it's wrong or anything, and this is the place to share what you want...
is that it just feels out of character. While it may not be a big secret for her and the Champ (and anyone Champ invites in, ie. Arona, Etheryn, Brint, etc.) her corruption-based libido is still something very personal and that she tries to hide from the public. She views the fact that the Champ bangs her as a blessing and a gift that they help her. Even when the two are caught in the throne room (by Lumia personally coming in), Lumia makes sure the other acolytes believe it's Elthara performing a ritual and helping Champ.
It just would feel careless and out of place for Elthara to slip up just anywhere, as opposed to it being caused by an interaction with Champ. For instance, she and Champ slip off into a closet and maid pops in, as opposed to her just banging a companion or other NPC and Champ finding them.
Again, just my thoughts on this one (which doesn't mean I don't like to imagine it either, it just doesn't feel 'right', unless the scene is absolutely amazing, of course).