What do you say to someone you don't like who won't leave you alone?

Not a memeber of the opposite sex, who's hitting on you,
but a co-worker that is a trouble maker.
I mean a cutthroat, gossiping, conniving person
who is so insecure that she needs to try and get everyone
in trouble just to boost her self esteem?

I mean someone who can't pick up on the sutle messages
that you don't want to have any relationship with them at all,
other than the business you have to do with them?

I mean someone who has to call or email you ten times a day
with nonsense, just to get attention?

I mean someone who keeps asking personal questions,
and when you tell her it's your personal business, she screams
"I don't know what your problem is with me?"

I have to find something to say that
is nonthreatening to this person that will get the message
across in a way that won't threaten her and that she can understand.