So tiny she'd be upset by deceit (10)
I believe the answer is:
dishonesty
'deceit' is the definition.
(I know that deceit can be written as dishonesty)
'so tiny she'd be upset by' is the wordplay.
'be upset by' indicates anagramming the letters.
'so'+'tiny'+'shed'='sotinyshed'
'sotinyshed' anagrammed gives 'DISHONESTY'.
(Other definitions for dishonesty that I've seen before include "fraud" , "Untrustworthiness, insincerity" , "Crookedness" , "Bad behaviour" , "Graft" .)