Well the first problem here is that it doesn't sound like you quarantined the new bird..so hopefully he doesn't have a disease and pass it onto her or you.
The other issue is that just because a hen shows courting behavior doesn't mean she needs to mate. On that note, if she was courting without another cockatiel around then she may be bonded to you and thinks you are her mate and she may not have any interest in the male.
Do you have any experience in breeding? It isn't something you just get up and decide to do one day. You need to do lots and lots of research and visit breeders who can teach you to hand feed. You need to be able to identify any problems the birds are having--if the female experiences egg binding and if they turn into a bondage pair versus a bonded pair. There is so much you should learn about before you set these 2 up with a nest box and let them breed.
Edit: Sorry if I sounded rude; a lot of people come here thinking their birds will take care of everything and that their won't be any complications. But, as breeders, people often have to intervene and take the hens to the vet to have eggs removed or pull the babies and handfeed them when the parent birds abandon the babies. I just don't want another person to assume that everything will be OK with their birds--since this will be their first clutch you may experience trouble since the parent birds are inexperienced and don't always get it right the first time. I just want you to be educated enough to handle problems if they arise.
IT WAS FUN.
Last edited by bjknight93; 03-05-2012 at 04:44 PM.