It is NOT her ‘duty’ to look after his parents (but obviously decent ppl make time for and look out for each other, regardless of the relationship)..
This rubbish about who comes first, who comes second is REALLY grates on me.. There would be a LOT less drama and fighting in families if people just learned to be a bit more fair-minded and objective.. Treating your parents well at the expense of your wife (or husband) is not the ticket to heaven..