usually it just is a deformity but can also be caused by temp spikes or be hereditary it can also be caused by the chick not positioning right in the egg.
you could try grinding the beak back and put deep food and water dishes for her but her case looks really severe that is why i say cull but give it a try you never know. usually this is for more mild cases there are people here that keep cross beaks but they require lots of attention so if you keep her be prepared to spend lots of time with her always grinding her beak possibly tube feeding her if she is a special chicken to you then try it!!!!