Shrink in the company of Queen (6)
I believe the answer is:
wither
'shrink' is the definition.
('wither' can be a synonym of 'shrink')
'in the company of queen' is the wordplay.
'in the company of' becomes 'with' (I've seen this before).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'with'+'er'='WITHER'
(Other definitions for wither that I've seen before include "Droop, shrivel" , "Dry up, shrivel (6)" , "Become dry and shrivel" , "Become shrivelled, lose freshness" , "Atrophy" .)