Museum to screen the Queen, and gallery (7)
I believe the answer is:
veranda
'gallery' is the definition.
('veranda' can be a synonym of 'gallery')
'museum to screen the queen and' is the wordplay.
'museum' becomes 'va' (Victoria and Albert Museum, or 'V and A').
'to screen' indicates putting letters inside.
'the queen' becomes 'er' (Elizabeth Regina).
'er'+'and'='erand'
'va' placed around 'erand' is 'VERANDA'.
(Other definitions for veranda that I've seen before include "Ground-floor extension" , "Roofed gallery beside a house" , "Sheltered terrace around a house" , "Roofed platform level with the ground floor" , "Roofed open gallery" .)