Most Helpful Girl
There's no way not to hurt her, except she doesn't have feelings for you. Just meet her alone and tell her. If you give her an explanation it would make it better (if she asks for it). Don't say "it's not you, it's me" cause it won't make anything better. Just be honest and don't avoid it for too long, the longer you wait, the harder it will become for you.
Most Helpful Guy
There is no easy way of telling her that you aren't interested anymore without inflicting emotional pain. However, you can ease the pain for her the more honest you are about your reasoning behind the breakup. It's one thing to breakup without a reason but a man has the courage to make the right decision and explain his reasons for making such an action. If you are truthful when breaking up, eventually she'll appreciate the fact that you were open and honest with her, whether the reason behind it had to do with her, you or both.