My advice is that you communicate with her what new feelings you think have surfaced in recent meetings but also voice your apprehension on ruining a great friendship. She will value this especially if you mention the recent highlights that you both have shared (assuming she truly does appreciate the friendship growth as you do), this way you have addressed the issue of this revelation being a potential risk of 'ruining a friendship'

You can also voice how the first time you asked her out was quite impulsive "...but after last night I'm noticing something that just felt different from all the other times we hung out" - as a start to you discussing it with her