There is no written statement. There is only the hearsay word of the husband who has plenty of opportunity for motves that are not in Terri's best health interests.
In addition, if there was a clearly stated intention for no life support, that usually applies to people who are brain dead and not conscious. This is not the case with Terri so killing her is at best assisted suiicide, which is also not legal.
Any casual review of both sides of this case simply reeks with ambiguity regarding Terri's condition and wishes concerning her state ordereed death. Therefore, as you say, life is the only viable and moral choice.
I call it "Involuntary Assisted Suicide", AKA "Going Dutch".