She's accepted responsibility for a minor crack (the dorm's affected) (9)
I believe the answer is:
godmother
'she's accepted responsibility for a minor' is the definition.
(someone with some responsibility for a minor)
'crack the dorm's affected' is the wordplay.
'crack' becomes 'go' (synonyms).
'affected' indicates anagramming the letters.
'the'+'dorm'='thedorm'
'thedorm' with letters rearranged gives 'dmother'.
'go'+'dmother'='GODMOTHER'
(Other definitions for godmother that I've seen before include "One in loco parentis" , "Stand-in for parent" , "Who's nominated" , "sponsor" .)