She is probably chaotic evil, but on the "selfish and overly-indulgent" end of the spectrum as opposed to "violent and dangerous." Her affinity for Roy disqualifies her from being neutral evil, since she probably wouldn't betray him, (chaotic evil often implies mass destruction and misanthropy, but given that the main defining aspect is unchecked indulgence, and Mimi clearly loves Roy, she'd never do anything to harm him as a result, because she enjoys being with him, therefore "indulging" herself with their relationship. Meanwhile, neutral evil focuses on pure pragmatism and holding any connections to other people is almost purely transactional.) and she also doesn't seem to hold herself to any code or standard, removing lawful evil from the equation.