Nan leaves in advance of guidance (6)

I believe the answer is:

advice

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'guidance' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for advice that I've seen before include "Opinion offered as to future action" , "Intelligence" , "tip" , "Recommendation for a course of action" , "Suggestion for appropriate course of action" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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