How can I talk to my aunt about end of life decisions?

Directly, before ill. End of life decisions are extremely important in people of all ages and health conditions. The best way to approach these matters is directly - it is important to discuss these matters open and honestly with our close family members. Printing out advanced directive paperwork to discuss (and review, sign, & witness) is a good place to start this conversation. Hospitals have staff to help with ad's.
Ask. Choose proper time & moment & mention others like friends or family & try to get herfeeling & wishes. Mention cases where people did not have directives & became subject to measures they would have otherwise declined or consented.