Musically, Jane was a disaster (8)
I believe the answer is:
calamity
This clue is a double definition.
'musically jane' is the first definition.
(Calamity Jane is a musical)
'a disaster' is the second definition.
('calamity' can be a synonym of 'disaster')
'was' acts as a link.
(Other definitions for calamity that I've seen before include "Martha Jane Cannary" , "Catastrophe" , "A sad or disastrous happening" , "Disaster, sudden great misfortune" , "Tragedy" .)