Dad keeps her quiet (3)
I believe the answer is:
mum
'quiet' is the definition.
(to keep mum is to stay quiet)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for mum that I've seen before include "Palindromic mater" , "Parent - shtoom" , "Mother (colloq.)" , "Quiet; relative" , "Tight-lipped" .)