Never mind her, you probably aren't ready to make any declarations if you get stomach aches just thinking about the idea of a date. Essentially, it comes down to getting over the fear of rejection, which is easier said than done.
I've basically gotten over it and, despite this, I get rejected all the time. In other words, confidence alone won't do it, even once you find the confidence to do it. Finding away to ask someone out, is one hell of a tough thing to do, especially with SA because, unlike other skills, it doesn't necessarily get better with practice, as your success depends on another person. It really doesn't get easier either; you just get more used to the idea of rejection.
I guess what I'm trying to say is take your time and work up the courage to asking her out to lunch before you write her a letter. She might reject you. She might not. Either way, getting rejected is the only way that I've been able to develop the thick skin to getting rejected. It's a bit of a catch-22.
Considering how I've felt when I've been in this situation, none of what I've said is all that helpful. Good luck, I guess. :idontknow:
Oh, and don't write a letter, sonnet, serenade, or manifesto about your love. It won't end well.