i wonder why she says thinks like that...
does she do that to everybody or just a few specific people?
i wonder what she gets out of it (negative attention better than no attention at all?)
i wonder if she does it when she is tired or when she is hungry...
i wonder if she has seen the behaviour modelled by other people in her life...

it might be that she doesn't know how to express grumpiness / frustrated feelings appropriately. kids aren't particularly good at knowing whats going on for them when they are that age... i think it is fairly common for that to be the case... that being said... how do her parents respond to her when she says things like that? do they find it funny? do they give her attention because of it? etc.