Can confirm that Katherine is an extremely fast writer XD
Another thing that helped is that we had a very clear roadmap before writing even began. Scenes were outlined and story beats laid out so we were able to jump straight into writing a scene without having to think much about where it would go. Having an editing partner that you trust takes off some of the mental burden that can come with writing. Even if my writing isn't perfect, I can trust Katherine to help me get it there. Much easier to enter a flow state that way.
And, ofc, LemonInk covering all of the programming was a HUGE factor in Katherine and I being able to write as much as we did. I was still adding dialogue on the final day which I never would've been able to do if I had to program it all myself. Us writers were truly spoiled for this one <3