An animal Her Majesty has to worry about (6)
I believe the answer is:
ferret
'an animal' is the definition.
(I've seen this before)
'her majesty has to worry about' is the wordplay.
I cannot quite see how this works, but
'about' could be 're' (regarding) and 're' is found within the answer.
'her majesty' could be 'er' (Elizabeth Regina) and 'er' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ferret that I've seen before include "Animal to hunt rats and rabbits" , "Animal trained to catch rabbits" , "silk ribbon" , "Small fierce animal, rabit hunter" , "Animal used to catch rabbits" .)