A good idea is too give it some cuttlefish (which you can get on the beach) and some hard kinda dangly things from a bird shop. Also don’t put a mirror in the cage because it can hurt itself flying into it. If it has red or white eyes it might be a bit scatty so its a good idea not to take it into the shower for a while.
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Congrats on adopting a cockatiel - they can be wonderful companions.
1. Stay away from chocolate, avocado, real sugary stuff, real salty stuff, real fatty stuff, most junk food.
2. You can start taking her in the bathroom with you from day one. Let her sit on a perch, cover the mirrors so she doesn’t try to fly into them, put the lid down on the toilet so she doesn’t fall in. (mine loved sitting on the shower rod).
3. She will twitter, chatter, squeak, squawk, scream, and grind her beak. This is all normal. They can be taught to talk and whistle, but are not as vocal as males and usually don’t do much talking or whistling.
4. make sure she has a cuttle bone and a mineral block. Give her a cement perch in addition to the wood perches to help keep her nails and beak trimmed. Give her lots of treats in addition to her main seed diet. She can eat just about any vegetable that humans can, raw or cooked. Fruits are also good. Meat in VERY small quantities and fully cooked is ok once in a while. Cooked eggs (scrambled with no salt or pepper or anything or boiled eggs). Cheese, yogurt, cottage cheese all in small quantities. Bread, pasta, beans, are all good. Chips, cheetos, pretzels, and other snacky stuff like that are really not to good because of the salt, but I would let mine nibble once in a while as a special treat. She would only eat about 1/8th of an inch of a cheetoh, or just a couple of bites out of the corn chips. It was almost like she had to taste everything I was eating. I still miss her. She was 19 years old when she became eggbound while I was at work and died before I could get her to a vet.
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Many Cockateils love scrambled eggs( shells and all) ! Its best if they are "Dry Scrambled" without oil or grease.
Crackers or toast are a real treat!
See if she likes fresh fruits and veggies. If so, apples, pears, cabbage, corn or green beans could be a hit. If she rejects fresh ones, try dried fruits and veggies like raisins, dates, prunes, banana chips dried cherries ,cranberries, apricots or pineapple. Cut then into tiny pieces about an eighth of an inch across because most ‘teils won’t wrestle with big pieces of tough leathery dried fruits. Another healthy favorite would be dried crushed hot peppers from the spice section of the grocery store. ‘teils love them, and they are very healthful for them.

Popsicle sticks are a favorite toy. They will chew them to pieces!! I buy them at Wal-mart for about $3.50 for 1000 stick in the craft section. You can just give her a handful or drill small holes in them and hang them in the cage from pieces of heavy cotton string.

Avoid scented products, like Glade air fresheners, scented candles or room deodorizers some of them can kill a ‘teil in a matter of hours!
Avoid bells or metal toys from China! Chinese bells and toys usually have high concentrations of zinc, which is toxic to ‘teils!
Avoid cherry wood or leaves. They contain cyanide which can kill a bird.

Wood from trees can be used for perches if you can get maple, Sycamore ,apple, or white pine. Beware of Yew wood, which is deadly. Sycamore is a favorite because the branches are twisty and have bumps and knobs which exercise their feet and toes! Just get a nice Sycamore branch and cut it with a small saw to wedge between the bars or corners of the cage. I change our perches several times a year. Its interesting for the bird, and free if you can find then proper tree in the neighborhood!

Good luck.
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Share my home with 8 Cockateils, one Lovebird, and one nearsighted Quaker Parrot who is convinced that we cannot see him being sneaky! Worked with a Vet for 2 years.