I think a brief "Happy Birthday! Hope it's special!" (or similar) e-mail is fine. Or maybe a Shoebox b-day card, with no note added, if you can get it to her WITHOUT PERSONAL CONTACT would be good too.
In fact, I think it's PREFERABLE if you can acknowledge the day (vs. no contact whatsoever), as it gives you an opportunity to do something that's MUCH LESS than what you would have done before.
What WOULD you have done before? What's your past history for b-days w/ each other?
