After a quick search, yes there is at least one incident of a woman who killed a boy and stated that she wanted to kill all men. There may be more, I haven't spent much time on the subject, either way the definition of incitement doesn't require anyone to follow through with the incited actions.

I definitely think that the person who killed a boy and stated that she wants to kill all men — I definitely think they shouldn’t have a Twitter account

Has Twitter been made aware of this person and won’t suspend their account?

valerie solanas comes to mind