I suggest making an eCard. Or you could make a written card and scan it. I believe poems are something you should include, but if you can't write one, that is alright. It is the though that counts, as they say. It needs to be something that has had a lot of effort put into it, then Katy would truly appreciate it, that is of course if she sees it. On the 29th, Katy is performing at the Sydney Opera House and I hear you can win a M&G with her. I'm planning on making a birthday card and see if I can give it to her then. If you live in Sydney Australia, then would be a great opportunity to hand it to her. However, if you don't, you can make a card on a program like Paint or something or make a card and scan it to her.
Hope I helped