Initially, Great Dane's upset when wife coming in gets bitten (6)
I believe the answer is:
Here is my best explanation:
'bitten' is the definition.
(gnawing is a kind of biting)
'initially great dane's upset when wife coming in' is the subsidiary indication.
I cannot quite see how this works, but
'wife' could be 'w' and 'w' is present in the answer.
an anagram of 'dane' is 'naed' which is present in the remaining letters.
A single letter 'g' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'gets' is the link.
(Other definitions for gnawed that I've seen before include "Chewed at like dog with bone", "Persistently nibbled", "Worried persistently", "Nibbled - chewed", "Bit or chewed persistently", "Wore away; champed" and "Bit persistently at something hard".)