There are many sort of people to make this imperfect world, more
or less complete.
You feel that they are destroying themselves - you did your best to
bring her to sense, nothing did. It is within their relationship
Karma that they have to go through, back up by first 13 years
childhood psychology impact and later years evironmental factors.

People finds it hard to even change bad habit (E.g. chopping
people, cooking curry, etc), what more someone who had been
receiving unconsciously reinforced messages from different factors
for so many years? 
You tried to do something - it is admirable and all you need to
know and matters is that you TRIED to do something.