Eris should have something down there she can use, but it has never been used or shown in-game.
It should've been visible in her scene, but I opted to make Eris more feminine overall, with her clit swelling only when needed.
Currently yes. Blackmailing Eris is still the "Eris Route," so you unlock her only current scene. It might not fit that well thematically, but it is still her only scene, so rather than doing the whole quest and not unlocking anything, at least the player gets something out of that.
Eris is a newish character and doesn't have a lot of content outside her quest, and because she can be taken off the game she has even less content compared to Sophie, who is permanent no matter what.