A user of the micro-blogging site told the pregnant singer, 'Your face makes me sick, you disgusting b****', to which Lily promptly responded, 'Then you should look at pictures of me all day, cause you look like you could lose a few'.
Obviously hurt, the user, who calls herself Olivia27x, explained that her friends had hacked her account and posted under her name.
Other users were quick to criticise Lily, 26, who herself suffered from bulimia nervosa in 2009, but she stuck to her guns.
'She was rude, and anyone who can't see that I was joking, well that's their problem,' she explained. 'I also have a right to respond to insults. Get off your high horse. I've never claimed to be a role model for anyone. I'll do and say what I want.'