The wiki is not an official source, it's colaborative (and mostly outdated). Therefore, any requirement that is not listed there is
not hidden.
You should refer to the dialogues above all else. All you need as information is theoretically in-game.
We'd need a screenshot of the refusal quote if possible.
A save before submitting her could be decisive also.
Feel free to make your own calculations and decide your objectives according to that.
Me I wouldn't grow a fiend just for that; I find it good as a way to train my assistant, and for food intake (fiend cum alimentation + fiend tatoo = epic win).
Also, you might have forgotten about the cryo cell. You're not forced to stick with one slave for 250 days unless I missed something.