Before appointment, oddly she becomes calm (6)
I believe the answer is:
sedate
'calm' is the definition.
('sedate' can be a synonym of 'calm')
'before appointment oddly she' is the wordplay.
'before' means one lot of letters go next to another.
'appointment' becomes 'date' ('date' can be a synonym of 'appointment').
'oddly' indicates alternate letters.
The alternate letters of 'she' are 'se'.
'date' after 'se' is 'SEDATE'.
'becomes' acts as a link.
(Other definitions for sedate that I've seen before include "grave" , "Composed and staid" , "not disturbed by passion or excitement?" , "Calm, not lively" , "Decorous" .)