Angel wing only occurs during wing development. Essentially what happens is that as the long wing feathers come in, they are filled with blood and therefore extremely heavy. Ideally, the tendons and muscles of the bird's wing develop strength about the same time and are able to support the weight. However, sometimes either the feathers develop too quickly or the muscles and tendons develop too slowly, and the weight of the feathers pulls the "wrist" joint outward at that odd angle. Even when fed exactly the same diet, some birds will develop it and some won't.
As such, no, it's not going to develop later in life. And wrapping tends to be highly effective.
As to what could have caused it, could you clarify her diet? Was she eating straight chick starter up until a week ago? When did you switch her to the corn/layer feed? Nine weeks, by the way, is too soon to switch to layer feed, for future reference.
The usual recommendation is to start cutting protein percentage in the chick starter at two weeks of age. By nine weeks, they would be eating about 2/3 chick feed and 1/3 oats or wheat or other food designed to cut the protein percentage. Layer pellets should never be fed until right before they start to lay around five or six months, and cracked corn is good only as a treat not a diet staple.
I hope something in here helps you. Good luck--the vet should be able to fix it and she'll be good as new.
