She will shortly be a nut case (5)

I believe the answer is:

shell

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'a nut case' is the definition.
'shell' can be an answer for 'case' (synonyms). I am not certain of the 'a nut' bit.

'she will shortly' is the wordplay.
'she' becomes 'shel' ().
'shortly' suggests the final letters.
The final letter of 'will' is 'l'.
'shel'+'l'='SHELL'

'be' acts as a link.

Can you help me to learn more?

(Other definitions for shell that I've seen before include "Protective outer case" , "Carapace or explosive missile" , "See 18" , "Protective outer casing" , "Walls of gutted building" .)

I've seen this clue in The Globe and Mail.

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