One appearing among the lady's legatees (5)
I believe the answer is:
heirs
'legatees' is the definition.
(I've seen this in another clue)
'one appearing among the lady's' is the wordplay.
'one appearing' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'among' is an insertion indicator.
'the lady's' becomes 'hers' (her refers to a woman).
'i' put within 'hers' is 'HEIRS'.
Can you help me to learn more?
(Other definitions for heirs that I've seen before include "They inherit property or rank" , "Successors" , "Inheritors" , "They get rank, property etc from others, perhaps their parents" .)