Well many reader devices can be converted to Chinese (I know the PRS-505 can), but e-ink is pretty suboptimal for displaying traditional Chinese characters.
You could always check out the Chinese website
http://www.mobread.com for general information. There are many things to consider when buying a reader. How do you plan to get books? What formats do you want to or expect to get? What kind of functionality do you want? Will she be reading simplified or traditional Chinese?
As a general rule, I am OK with English books on my PRS-505 as long as I can convert them to a more pleasant PDF. Chinese books I tend to only buy in paper format (though I understand that's not always very convenient). I've tried a lot of different ways to get my Chinese ebooks up to snuff visually, and e-ink just doesn't cut it for me. However, if she is OK reading very large text (probably 15pt or bigger), it's not bad.
Addendum: Just tried out some 12-16 point fonts, and a few are OK at 12, most are OK at 14. Feels odd reading such huge type when all of my books are just fine with smallish text that is still highly readable.