In my opinion the writing is the one thing I don't think she can hire someone for. Maybe helping her with basic ideas (depending on what she does or doesn't have planned yet, although I assume she has it pretty well planned), or preliminary drafts providing the final draft is Eva's -- because it'll be noticeable if it's not, and not in a good way -- but that would probably be the extent of it without the player's experience suffering in varying degrees (mostly in the way of immersion).
Nobody has the same 'voice' (unique, personal style of writing) as Eva, nor would anyone understand the characters and plot as intimately as she does - especially as all characters and author creates embody some aspect of themselves, or an aspect or personality they feels emotionally connected to in some way, which no one else is going to understand in the same way). It's Eva's plotting and execution through her writing that gives the game its unique tone (and make the sex scenes so good), and what sets this game above most, if not all, other adult games on this site; what take it from being 'just another adult game' to making it stand out as an example for what a great adult game can really look like.
So yeah, I really hope she doesn't hire anyone to help her write - pretty much every game I've seen with multiple authors feels disjointed from one author's writing to the next, or has you favoring one part that a specific author wrote (whose unique voice resonates with your taste) rather then allowing you to enjoy the game as a cohesive whole.
Again, this is in my opinion, and from my experience.