(1) Do you know any friends of hers?
(2) Do you know those friends of hers?
(3) Do you know a friend of hers?
Both in (1) and (2), ‘hers’ seems to be ‘her friends.’ But in (3), is it ‘her friend’ or ‘her friends’? If ‘of hers’ has a meaning of ‘among the set of her friends,’ it would be the latter. While if it has a meaning of ‘that is her friend’, it would be the former. But this so called double genitive (CGEL,p.46, fn. 63) makes me wondered.