First off, I wanted to distinguish the two Felicias, and so took a cue from Spider-Man: Web of Shadows to give Felicity a symbiote--pretty much entirely for tentacle and or futa sex somewhere down the line.
Darla Deering was there because the plot called for, well, a rich bitch and she seemed a plausible enough candidate and not "in this universe, Kamala Khan is a celebrity!" I read somewhere that she's based on Katy Perry, so that's where I got the idea for the dress, just with a 'Sexworld' twist. It is kinda handy that when you're trying to describe how Not Katy Perry looks, you can just say "she looks like Zooey Deschanel!" Work smarter, not harder.