They already did that by hiring people to make the backgrounds and some of the colouring, and have talked about hiring someone to help out with the line drawing. But to be fair they’ve used that to improve the quality rather than speed up the development. I guess it’s also possible to hire more help with the code or the job of finding reference images, but it’s probably true that it’s limited how much more they can speed it up without losing some of the creative control of the project.
Speed comes down to two major factors now: Money and trust (well, and planning of course, but I wanted to simplify). If Eva can find a line-work artist who she can communicate with well with and whose style she has faith in, that's where the trust comes in. Artwise, she can still select and edit/collage the photos she wants to use + dictate the tone, mood and style of the art produced, as she somewhat does now with the colorer she uses.
The money factor comes into paying for the right lineworker talented enough as well as paying for a full-time coder, full-time production manager (including coordinating marketing, legal, business communication (with steam, ect) and day-to-day with freelance staff), a full-time paid QA lead who can also pick up slack elsewhere as needed (maybe one who's a proficient writer, to clean-up disjointed path text + potentially help her look for reference photos from her set specifications), plus the purchasing of game assets (like better music, sound effects).
With 3-4 trusted, proficient full-time staff members and a few talented freelancers, I can see the game slice at least 2/5 to potentially over half off development time for each update for updates roughly every 3 months or less, with better overall quality too. Giving guidance, Eva could still have full creative control. But she'd have to trust the staff enough to take over the day-to-day minutia so she can focus almost 100% on storylines and creative direction. Creative direction: Just because others are doing the actual linework and coloring doesn't mean she needs to accept whatever output they turn in. "This expression is a little off. If you could just... What I had in mind was.. The overall ___ should be.." And yeah. She'd probably have some time to still sketch some key scenes herself if a certain scene was "hands off. mine" or just something hard to communicate.
Of course, relinquishing some of the minute control may be hard for her as her background is primarily as an artist.