No postcard. How about a telegram sent when you know she has finished the presentation? Say something like:
Congrats! (stop) I know all your hard work paid off (stop) I'm very proud of you (stop)
Or, after the presentation, have room service deliver her breakfast: croissants, coffee, juice, flower etc. But of course you need mucho information, like where she is staying, for how long, and verify it with the hotel. Of course, you will have to arrange it with the concierge. You give them a credit card number, so it won't appear on her bill.
