And also, given that the parents visit her frequently and see all the things and more that we've seen in the video, why did they admit that they knew their daughter was PVS?
Because they had consulted with the gazillions of doctors and therapists who treated their daughter and knew that after 3 months, there's never been anyone who has come back from PVS.
I don't know of too many folks, if anyone, who expects Terri to "come back" (fully recover) from whatever damaged state she's in. But there's hope among many that she'll respond to treatment - treatment that has been denied for a long time.