After university we'd threaten her appallingly? That's a bit sick! (5,3,7)
I believe the answer is:
under the weather
'a bit sick' is the definition.
(under the weather means a bit ill)
'after university we'd threaten her appallingly?' is the wordplay.
'after' means one lot of letters go next to another.
'university' becomes 'U' (abbreviation for university).
'appallingly?' is an anagram indicator (I've seen this in other clues).
'wed'+'threaten'+'her'='wedthreatenher'
'wedthreatenher' with letters rearranged gives 'ndertheweather'.
'u'+'ndertheweather' is 'UNDER THE WEATHER'.
'that's' is the link.
(Other definitions for under the weather that I've seen before include "where you have to look for this crossword?" , "Indisposed" , "Sickening" , "Out of sorts" , "with clouds gathering overhead" .)