Will this work

I want to LD and in my LD i want to kill this girl. I hope this to signify the fact that I have killed her out of my mind and my feelings for her have gone. Will killing her in LD remove her from my mind so I don't keep thinking about her?

It's your mind, so if you truly believe it will, it will. The fact that you're asking here means your faith is a little shaky though, so try it and see.

So you want to use your LD to get over a girl, correct?

To be honest...I'm not sure if "killing her" in your LD will bring about the results you would like. Murdering someone in a dream isn't going to magically erase that person from your mind. You need to deal with it, deal with your feelings, rather than resorting to violence. I'd think that there would be alot of other, better, more peaceful ways to help yourself to get over someone without having to kill them.

I have already tried asking her to go away but she won't and she runs too fast before I can do anything! then well my dream finishes and if I speak to her she don't wanna talk to me. Its like in real life with her and me, sigh I did like her once.

I have had many violent dreams against people I hate in real life. Oddly enough, I find that it does help me cheer up and not hate them so much.
I remember when I was in school there was this girl I hated with a passion. Her name was Laura. And one night I had a dream I was watching her play soccer and this guy she was playing against was strangling her so violently, she passed out and perhaps died. I woke up *almost* crying and ever since that dream Laura doesn't bother me that much. lol.

Don't worry. Ignore her and she'll go away. That's how basic psychology works. If she doesn't go away, you aren't ignoring her long enough. That would be the best approach.

A more interesting approach would be to transform her into someone (or something) else.