Just an update: I received an offer of publication for the novella with Entangled, from a different publisher. I let them know and they responded within a week with a lovely little rejection. There were many things they liked about my book--mainly the tropes and my writing style--but felt the conflict wasn't strong enough. Good, constructive feedback, together with the editor's direct e-mail to submit again should I have anything suitable. Plus a sincere congrats on my other offer. If I write something suitable for them I'll certainly submit.