My question is: Can libel to stop the crime against myself be sued?

I've been harrassed and annoyed by my roommate for 2 years and 6
months. Finally I moved out to another room, but she continues to
contact me in spite of my request of not to do so.Because my health
gets worse as the results of her stalking, I asked help from the
ombudsman of the school many times for nothing. I emailed her that I
would tell everybody why you shouldn't contact me if she did it once
more. She did. When she did it again, I emailed her persistent,
annoying behaviors to my schoolmates. I inadvertently added in
parentheses that she had a sexual relationship with a man for 10
years, which is true,
while describing how obsesseively she annoyed me, even with the
question about that man's intention of carrying her photo. I never met
him and know nothing about him.

Today I came to know that stalking is a crime. I wrote it to stop the
crime which I didn't know it is at that time. As mentioned above, I
let her know I would before

Libel is:

 "...publication of a false statement of fact, made with the requisite
state of mind, that causes injury"[1].
http://en.wikipedia.org/wiki/Libel

  Meaning - if you can proove it is true - it is not libel.
  Proof of truth  would be a defense in a libel suit.

  Stopping a crime would not be a defense: You cannot take into your own hands
 - except in case of emergency :
        APPROPRIATE self-defense against a PHYSICAL attack.

Some people use words 'self-fefense' in broader sense
 http://people.howstuffworks.com/vsd.htm
but legal profession expects you not to engage in self-defense unless
you or your property is in immediate danger, such as attempted robbery
or rape.
 http://www.nononsenseselfdefense.com/

 That said, here is an suggestion. This service does not provide legal advice
 - see disclaimer at the bottom of the page. So making a suggestion means that
 it does not look like a legal issue, it does not look like a
stalking, it does not look like a any crime was commited by either
party.

  You did not stated your gender (I suppose you are both girls) and 
  that you are student at a US college, probably a foreign student?
 
Suggestion: Calm down. Your case (based on your incoherent description) is weak.

 No one will take seriously assertion that you were harrased
 "for 2 years and 6 months .. " and did not move out sooner.

 Moving to a different room is a first thing a reasonable person would do
 when roomate situations is not pleasant.

Ombudsman probably ignored your complains because your description looks
so emotional and confused.  Find a counselor, if necessary a psychologist
available through a health plan, and discuss the issue with him/her.
 
And no matter what you, do not publish any more negative comments about her;
(true or false). It will not have desired effect, and it will not make
you look good and be popular with other students.
If all you are getting are unwanted emails, just delete them and ignore them.

 If the emails are properly signed, sending them is not polite,
 but not illegal either. You may set up a filter, which will automatically
 send them to trash. Ask your SA (system admin for help, if necessary).
http://en.wikipedia.org/wiki/Spam_filter

Chances are that unwanted mails will stop  in a month or two, if you ignore them.

Hedgie

Hello Acorn

Hedgie is absolutely correct: two wrongs don't make a right.

You don't mention your age - which could be important.

However, you must find some way of sorting out your differences with
your former room-mate.

Perhaps there's someone in your class who can knock both your heads together?

The word 'Sorry' can also work wonders.

Cheer up

Bryan

Are you older than 12?