I hope you were very clear with her. It's your duty ... both to her and to yourself.
Someone said you should give her the option of just being your friend. I don't think that will work ... she will probably grasp at any possibility to keep close to you.
I hope you were kind, but said with no equivocation at all that you're definitely not interested.
Let us know what happens.
This has happened to me five or six times (not recently), and trying to be too tactful at the cost of clarity, always extended the agony.
I will