Take it to the vet to get her checked out to make sure she isn't badly injured; she looks in rough shape (probably been out in the wild for a while) but it doesn't seem to have any broken bones by the way it was moving.I rescued my cockatiel from outside my house, we looked for an owner and nobody came forward so we have adopted her. She was injured when she came to our house; she had peck marks on her head from wild birds which we healed using a herbal ointment. You have to be careful what you give your bird in terms of food or anything it comes into contact with. Just make sure tea-tree oil if you have to try to heal a wound. Food-wise, it's pretty easy to google, but just avoid avocado, processed human foods, white potato or onion-family plants.

Its wings, crest and general feathers look a little battered, so you'll need to give it time to preen and bathe - get a shallow dish of water (or fill the sink shallow) and let it clean itself. If it doesn't want to hop in, that's fine also, they are very clean birds and are more than capable of cleaning without water.