Rabbits are sentient beings in real life, but in game sentient probably refers to dwarf fortress sentients:
http://dwarffortresswiki.org/index.php/DF2014:Dwarf#Ethics Dwarves will not butcher creatures with the sentient tag (elves, kolbolds, humans, goblins, animal men). Killing a worker would be really demoralizing in my opinion and the other game NPCs would probably freak out.
Edit: See everyone's posts on how there is indeed a ridiculousness amount of unknowns to who is the most guilty I think we should warn both of them, return things to the status quo (give grog back), and not heal any of them. Whether to solve it with brain scanning, if it is non-invasive and completely safe we should do it, but I'm afriad if it is dangerous and we get a bad omega magic roll:
What you find is not terribly impressive. Marelflare is almost completely lacking in ambition, and although she is clearly very bright, also seems a bit deficient in the common sense and free will departments. You know enough about imps to know that most of them are flowing over with mischievous energy, so you suspect that Jorgen must have used ego magic to mold her into a better apprentice. Or one of his students; If Mareflare is the victim of a mind tinkerer, who ever worked the spell was unsubtle and clumbsy enough to cause a good bit of collateral damage.
We'll get brain damage people.