Little girl following Jack's elder sister (6)
I believe the answer is:
abbess
'elder sister' is the definition.
'abbess' can be an answer for 'sister' (thesaurus). I'm not sure about the 'elder' bit.
'little girl following jack's' is the wordplay.
'little girl' becomes 'bess' (I am not sure about the 'little' bit.).
'following' says to put letters next to each other.
'jack' becomes 'ab' (both can mean a sailor).
'bess' put after 'ab' is 'ABBESS'.
Can you help me to learn more?
(Other definitions for abbess that I've seen before include "Head of convent" , "superior to her sisters!" , "superior lady" , "Principal of convent" , "Superior of group of nuns" .)