Mother meets her end in ruin! (3)
I believe the answer is:
mar
'ruin' is the definition.
(I've seen this in another clue)
'mother meets her end' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'meets' means one lot of letters go next to another.
'end' suggests the final letters.
The final letter of 'her' is 'r'.
'ma'+'r'='MAR'
'in' acts as a link.
(Other definitions for mar that I've seen before include "Oh dear!" , "Spoil or deface" , "Detract from" , "Spoil stuff" , "Spoil, damage" .)