Terri IS a Catholic and this IS against her religion. Using the qualifier "practicing" does not make it okay. Apparently, she did not attend church regularly before her collapse, and sadly, many Catholic young adults do not attend church regularly, use birth control, etc... But that does not make this okay in the eyes of the Church. The parents tried to make this argument, but it fell on deaf ears. Religion has no weight in our society.
I really wouldn't care if she actually did want to be starved to death. Nobody has a right to commit suicide. Starvation is not a natural cause of death.