Cho Chang is a valid name.
Firstly, it could easily be transliterated in Wade-Giles which is not uncommon in Britain and amongst Chinese diaspora (example Peking rather than Beijing).
Second it can be a transliteration of a dialect, of which Chinese has hundreds.
Thirdly, two character names are not uncommon either. My own full name (not my username) is two characters. Equally when in the West it is common to put the family name last even though that isn't how we do it typically in Chinese. When in Rome...
Fourthly, just because a name is rare or unusual doesn't mean it's not ok to use it. There are weird and wonderful names all over China I can assure you.
Fifthly, if her parents were inspired by other cultures to give her that name, what then? Must she remain 'culturally pure'? My eldest has a Western name that I love, should I immediately repent?
And finally, as another poster has pointed out... there are literally people with the name Cho Chang!