Unequivocal suicide...

She killed herself, and the mayor, who we know was the puppet master of the town's entire legal/law enforcement system, simply had his cronies doctor the crime to make it look like he killed her. The question thereafter would be, Why? After all, he had "taken care" of the lawyer, and Kolya had, with no other choice, ceded defeat. The Mayor, as a gesture of pure evil, felt the need to teach Koyla one final lesson. Koyla was insolent in creating the unnecessary stress he (the mayor) experienced from the whole affair, and from the Mayor's perspective, Koyla, a mere insect, should have known his place and moved out of the way of the Leviathan.