Get her to talk about her problems.
Usually the desire for death is really the desire to escape from pain which seems inescapable. Focus on helping her to find alternative solutions to heal the pain; ask her the questions that enable her to find the answers for herself.
Keep in touch at least once a day, and keep talking until its clear that the crisis is past.
Often, just having a friend who cares is enough.
recommend The Samaritans (on line, but has telephone service in USA and UK).
Get hold of some statistics... people who have had other who commit suicide in their lives are much more likely to do it themselves... give her a shot of reality that what she does matters and affects others.
Tell her how it would affect you and the others around her if she does it.
In the end we cannot actually stop anyone who is really serious about it.
if she does it, don't blame yourself, because ultimately it is her choice.
If she told you then she wants you to stop her..that's usually a cry for help.
Hey look it may not be that she doesn't like you, if she is how I feel she is then she hasn't got many emotions going on other than deep sorrow, hurt, and anger, that tends to make people seam indifferent toward you. I can tell she really cares about you because she told you that...she is- weather she admits it or not- searching for love, understanding, purpose, and someone in her life. Whatever you do don't stop talking to her don't ignore her. She obviously knows you care...she is in her own way asking you to help her.
I've been where she is...she really needs someone she can talk to, someone who will love her, and not for her physical person, or pity, but because of who she is. You need to tell her why you love her. Try hugging her and talking to her. If she will talk to you listen and offer the best advice you can, just try and let her know you really care and you aren't talking to her out of fear of feeling guilty later. I'll pray for you.