Share with your relative the scriptures where Jesus says that "we desire mercy not sacrifice " Mathew chapter 12 I believe the. In Mathew chapter 15 he says "nothing entering into a man can defile him" then explain that in the 70s jws were told not to have any transplants for that was canabalism yet just 13 years later they changed thier minds. Then maybe relate to the new WT where they say they are neither inspired nor infalable .
I think she will die if you don't try since no other JW will be excepted. One last thing you may relate to her that they allow cows blood as per a KM so you may ask why is cows blood ok but not human, you also may add that in human breast milk there 1 million white cells per drop.