New Delhi, March 27 -- Samara Martinez has written countless letters to the illness that weakens her body.

"Dear cursed one," the Mexican activist once wrote. "I hate you because you have taken things away from me, but I love you because you have been my greatest teacher."

At 31, Martinez is among the most prominent voices pushing to decriminalize euthanasia in Mexico. The topic has long been debated by advocacy groups, politicians and academics. However, her case has shifted that conversation into the public spotlight as lawmakers weigh possible policy changes.

Martinez developed early signs of chronic kidney failure at age 17. Despite chemotherapy, two kidney transplants, dialysis and frequent hospitalizations, her prognosis estimate...