Her impairment is cognitive and Judaism does not recognize any less of a right to treatment for one cognitively impaired than one mentally astute.
It is a denial of the Jewish ideal of the fundamental value of life that drives the forces that wish to remove Terri Schiavo's feeding tube. While Judaism does recognize quality of life in certain circumstances (such as the incurable terminally ill patient in intractable pain mentioned above), the Torah does not sanction euthanasia in any situation. To remove the feeding tube from a patient whose only impairment is cognitive is simply murder.
Let's hope that this cruel murder by starving will not take place!