Grandma’s wise, so many (not all) reflecting (5)
I believe the answer is:
moses
'grandma's' is the definition.
(I've seen this before)
'wise so many not all reflecting' is the wordplay.
'not all' indicates a hidden word (only some of the letters).
'reflecting' says the letters should be written backwards.
'sesom' is hidden in the letters of 'wise so many'.
'sesom' in reverse letter order is 'MOSES'.
(Other definitions for moses that I've seen before include "Great Jewish leader who led the flight from Egypt" , "Prophet found in a basket" , "the tablet-taker?" , "Prophet of the Old Testament" , "Grandma __, American folk artist, d. 1961" .)