She means a lot to dad (3)
I believe the answer is:
pam
'she' is the definition.
'a lot to dad' is the wordplay.
'a lot' becomes 'm'.
'to' says to put letters next to each other (I've seen this in other clues).
'dad' becomes 'pa' ('pa' can be a synonym of 'dad').
'm' after 'pa' is 'PAM'.
'means' is the link.
(Other definitions for pam that I've seen before include "Female" , "- Ayres, English poet" , "Short girl's name" .)