new contact invitation

Hi all, just installed WhatsApp and have a problem. I have a friend from Brazil, she gave me her number and said that she uses WhatsApp. I created a new contact, added the 5511 code followed by the 9-digit number she gave me and refreshed contacts in WhatsApp. Anyway, I am suggested to invite the contact to WhatsApp (Check out WhatsApp Messenger for your smartphone etc.). Does it mean that the number I entered does not have WhatsApp or maybe I entered the number in a wrong format? Shouldn't WhatsApp tell me if there is such user?