多謝指正按照我在133楼引述的英国政府官网的解释，你母亲是不可能申请BNO的，但有可能申请British Overseas Citizens:
If you were a British overseas territories citizen only because of your connection with Hong Kong you lost that citizenship on 30 June 1997 when sovereignty returned to China.
However, you became a British overseas citizen if either:
you had no other nationality and would have become stateless
you were born on or after 1 July 1997 and would have been born stateless if one of your parents was a British national (overseas) or British overseas citizen when you were born.
The different types of British nationality explained - British citizen, British overseas territories citizen, British overseas citizen, British subject, British national (overseas), British protected personwww.gov.uk