She puts lb50 on the nail, possibly (6)
I believe the answer is:
lilian
'she' is the definition.
'lb50 on the nail possibly' is the wordplay.
'lb50' becomes 'li' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters goes inside another.
'possibly' indicates an anagram.
'nail' with letters rearranged gives 'lian'.
'li' inserted into 'lian' is 'LILIAN'.
'puts' acts as a link.
Can you help me to learn more?
(Another definition for lilian that I've seen is " girl".)