On their drive she happens to see Mikhail, and chooses him to be her partner in what begins as a completely impersonal experience.
The uncomfortable scene in question here occurs at the end of Requiem for a Dream, when each of the main characters are deep in the worst chapter of addiction.
Clive, meanwhile, clearly finds Dren Delphine Chanéac beautiful, although she's more animal than human with her giant eyes, long tail, and feet that look like hands.
So they go to a construction site and do the deed in a giant metal pipe, doggy style.