I'm treating my girlfriend for her 21st birthday to Cirque Du Soleil. Tell her or leave it as a surprise?

Should I tell my girlfriend that her birthday gift is going to be Cirque Du Soleil, or just leave it as a secret till the last minute? She may never even have heard of it and may not know what it is. I have already purchased the best tickets and we are five days away from seeing it. If I tell her in advance she can learn about what it is, and perhaps enjoy it better, but I'm not sure if this is a good move on my part. Is it better to surprise her? Any help will be appreciated. Thanks.