I was in the same situation as you once. I felt all tongue tied and didn't know how to express it in words, so one day I just kissed her. We've been married almost 15 years and are still best friends. But results may vary.
You should be careful. -Say that lately you feel "attracted" to her and you wonder if she feels the same way?" -Don't use the word "Love." -You want to give her a way out, if she doesn't feel the same. -You may want to keep your friend and find another love interest. Good friends are hard to find.