Raise a glass to Her Majesty’s kitchen assistant? (7)
I believe the answer is:
toaster
'kitchen assistant?' is the definition.
(kitchen appliance)
'raise a glass to her majesty's' is the wordplay.
'raise a glass to' becomes 'toast' (to raise a glass to someone is to toast them).
'her majesty' becomes 'ER' (Elizabeth Regina).
'toast'+'er'='TOASTER'
(Other definitions for toaster that I've seen before include "Machine for making brown bread?" , "Kitchen gadget" , "One raising glass" , "Health-promoting" , "In the morning, this device used" .)