She's a saint, taking a long time penning short note (5)
I believe the answer is:
agnes
'she's' is the definition.
'time penning short note' is the wordplay.
'time' becomes 'ages' (I have seen 'Long time' mean 'ages' so perhaps 'time' could also mean 'ages'**).
'penning' means one lot of letters goes inside another.
'short' suggests taking the first letters.
The initial letter of 'note' is 'n'.
'ages' going around 'n' is 'AGNES'.
'a saint taking a long' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for agnes that I've seen before include "Tube for cables" , "David's second wife" , "lass" , "Woman" , "Miss Grey" .)