What to do when a girl tells you this..?

Wow :/ how super sweet of you to not want to be a jerk to her. I can see why she likes you so much. It is sad that she would go to such levels to be with you and that she does not have more respect for herself, but dont tell her that! That is just between you and me. You are very nice and I would suggest that you tell her that you are very flattered, but you are not interested in her at all. Be completely honest with her. If you have to say something negative to someone you can pad it with a positive comment first if you want to be helpful. Another example is " you are a very nice girl, but I am completely not interested". That is honest and it is not being a jerk. If she continues, just keep repeating yourself. She will eventually get it. Sometimes people have to hear the word no or have to hear something at least 3 times before they get it. Good luck my friend :) and good job not being a jerk. There's enough of those in this world, and its nice to see that you are not one of em :)