She's not a day over thirty! (4)
I believe the answer is:
june
'she's' is the definition.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for june that I've seen before include "Month of our summer solstice" , "Month named after Jupiter's wife" , "some time" , "Month after 14" , "The "flaming" month?" .)