I think they're doing the right thing. The only part of her brain that still functions is the brain stem which takes care of automatic functions (heart beat, breathing). She has no concept of herself, her parents are holding on to false hopes.

She's been a vegetable since 1990, there's lots of people on these boards who were born around that time. Even in the impossible reality that she some how repairs her severe brain damage and becomes lucid, how do you think she'd deal with missing 15 prime years of her life?

Who here would like to be artificially fed by a tube for 15 years? I know I wouldn't. If I ever become a vegetable I'd hope my tube would get pulled, sending me packing into the great unknown. Not clinging to a damaged, unconscious body for decades.