I wouldn’t do it in Italy personally.
to be honest I’m pretty certain your wife will be able to get a spare, good chance this drops to all members and even if it doesn’t they’ll be tonnes flying around.
Might be plenty of spares, yes
But in Italy it is law that the name on the ticket must match the passport.
and they will certainty be several checks at the San Siro, like every other Italian away in Euro.
Plenty have sat in the home end in previous games*, you can tell as the game finishes when they all leave and ours hang around.
Its down to personal choice.
*Not sure how they get around the name checks etc