I am sure Cameron wasn't aware of what was printed on her bag otherwise she wouldn't have wear it. Just a stupid misstake which could be avoided though.
To be honest when I go abroad and I don't speakt the language of the country; I am NOT less careless than Cameron. And chinese is not a common language that you could maybe understand or trying to read. So I don't blame her for doing this terrible misstake especially because she apologised.