Should I write her a letter?...?

My friend is leaving for the Air Force. And, I plan on going that same route (but it's post poned for now for medical reasons) . We'll hang out tomorrow, but she leaves in couple of days-so I was thinking of writing her a lettler and just reminding her that if she ever needs be I'll be there for her. This letter would just be a lot of things that I mkight forget to tell her or she should know, she can read this as she is on the plane etc. Should I do it?.. I want to, I think she'll give me her addy so I can write her, but I'm not sure. I don't want to make it too emtional-but it's so surreal how she's grown -up and stuff.