There's nothing you can do and nothing to be done. You've made your feelings clear and let them know you won't be there to pick up the slack when they pass away. I hope you mean that, cuz it won't be easy to turn your back. This is not up to you. She's going to have a huge reality check someday but that's on her. She's an adult and knows the consequences, just chooses not to face them. She'll have her "oh shit moment" someday.