There will always be hurt feelings; you cannot prevent those any more than you can prevent rain from falling from the sky. All you can do is be kind.

In your shoes, I might send a short message explaining I think she's a wonderful person but cannot continue our friendship due to my strong romantic feelings. I would also wish her the sincere best of luck in the future. I would make clear that this was my last message to her; that I was not expecting her to respond in any way; and that I myself would not be communicating any further as well.

Closure (from the universe) is a myth. Real closure is something only you can give yourself. Don't get stuck on closure; it's just the reflection of the moon in the water.