Our queen, looking back to girl as a princess? (5)
I believe the answer is:
regal
'as a princess?' is the definition.
(regal means relating to royalty)
'our queen looking back to girl' is the wordplay.
'our queen' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'looking back' shows that the letters should be reversed in order.
'to girl' becomes 'gal' (synonyms).
'er' written backwards gives 're'.
're'+'gal'='REGAL'
(Other definitions for regal that I've seen before include "Kingly glare?" , "Royal - 5 down (anag)" , "Grand and imposing" , "Befitting a monarch" , "King's" .)