If you think that your cockatiel may have ingested a potentially poisonous plant or substance, call your avian vet as soon as possible or better yet, just take your bird right away to the vet, as there is no time to waste.
It's very important that your cockatiel has a good source of calcium (like cuddle bone fish, commonly found in pet stores) , plenty of fresh water and even vitamin supplement for cockatiels.
"99% of Indoor plants are poisonous to cockatiels"
Birds have a super fast metabolism and if your bird in fact has consumed any poisonous plant, you do not have much time left. As with any animal that you are caring for, whether is a cat, dog, or bird, always have handy the phone number of your preferred vet (avian in this case would be best), and an additional number of a 24 hour vet clinic that is closest to you, just in case you have a tragic incident after hours.
As always the information offered here is to provide guidance and is not intended to be a substitute for the good advice provided by your own avian vet. When in doubt always consult your own veterinarian.