my cockatiel is been picking her feathers, what to do

she started loosing her feathers a month ago, the veterinary said, is because her nutrition, she got vitamin E & D shots, three weeks ago, I feed her with seeds, I got oil with vE, she likes pop corn, tortilla, bread. She is not improvement , the last two days she's been picking her feathers a lot; when she shake her body or fly, the feathers come off ezly. Now the doctor said, "she is under strees". She got done diferent tests and these are ok. what to do, she is not the same than before, heeelp! I don't want her to die.

If the vet said its nutrition, is that the main part of her diet, seed?

If so there is part of the problem.

Main food given should be varied from fruits, vegies, pasta, rice, egg, grain, pellets, some live food now and again.

(apple, pear, mango, small amounts of water melon, grated carrot, spinach is a fav, corn on cob, broccoli, silverbeet, mung beans, snow peas, multigrain breads, fruit breads, boiled egg, madeira cake as a treat once a week?, cooked pasta, cooked rice, mix this with some apple or egg, if your cockatiel is solely on seed she will be very reluctant to try anything new, but keep trying anyway, lower the amout of seed and add some pellets to it.

Add 2 different bowls of fruit or veg, whichever u prefer.

Never give avocado, this is toxic

Never give lettuce, mainly water, no nutritional value.

Stay away from cabbage aswell, this dosent seem to go down to well.