Rosie's mad with us for being difficult (7)
I believe the answer is:
serious
'being difficult' is the definition.
('serious' can be similar in meaning to 'difficult')
'rosie's mad with us' is the wordplay.
'mad with' indicates anagramming the letters.
'rosie' mixed up with 'us' can make 'SERIOUS'.
'for' acts as a link.
(Other definitions for serious that I've seen before include "Earnest, sincere" , "Important -- grave" , "Stern" , "Earnest - important" , "Earnest; vital" .)