With reference to your point about Chinese exit visas the Sino-British Joint Declaration of 1984 specifically states
that 'The Hong Kong Special Administrative Region Government
shall maintain the rights and freedoms as provided for by the
laws previously in force in Hong Kong, including freedom,
of movement
Furthermore 'Unless restrained by
law, holders of valid travel documents shall be free to leave
the Hong Kong Special Administrative Region without special
authorisation'. The words restrained by law refers to those persons subject to restraint orders by a court, eg bail. The right of freedom of movement is also included in article 31 of
China's Basic Law on Hong Kong. As you can see therefore your
wife will not be subject to any exit controls after 1997 but
will be free to leave Hong Kong at any time provided of course
that she has the necessary travel documents.
bl.art.31.BTC
SLM