Interest single mother initially showed in fake diamonds (7)
I believe the answer is:
pastime
'interest' is the definition.
(I know that interest can be written as pastime)
'in fake diamonds' is the wordplay.
'in' is an insertion indicator.
'fake' becomes 'paste' (I've seen this before).
'diamonds' becomes 'im' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'paste' going around 'im' is 'PASTIME'.
'single mother initially showed' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for pastime that I've seen before include "Hobby; regular activity" , "Leisure pursuit" , "relaxation" , "Hobby - recreation" , "diversion" .)