爆谷

do u mean you cover her cage from 8am-6pm everyday?
if so, it's really too long.  i don't think she will be happy.
even if this dosen't cause physical problems, it may make her mentally ill.

does she scream for a long time, or just for a short while?
perhaps you give more information, so that people here can give proper advice.
(e.g. species, age, gender, how long u've kept her, how long does the problem last, etc).

*tips: u will likely get more feedback if you can type in Chinese.

爆谷

10# bennyfung
covering the cage for 13 hours sounds long. but books mention that parrots need 12 hours sleep. so i guess the point is how you interact with her during the day.
does she stay at home on her own?
if someone's at home, does that someone interact with her?
does she have enough toys?
how's the quality and length of time you spend with her?
the point is, she already have 13 hours in the dark alone, she needs some company during the day.  but that doesn't mean playing all the time. that can be as simple as watching TV with u , sitting next to when u r surfing the net, etc.
wish your cockatoo a happy life.
*sorry to ask again, can u type Chinese? can u read Chinese?

爆谷

10# bennyfung
strongly recommend u to try the method mentioned above by shirley. good luck!