The court ruled this to be the case, and was upheld at every level of the state and federal judiciary.
Not only is it based on (English) hearsay
No, it was based on testimony.
Hearsay is hearsay, in real life, no matter what FL rules are. It's a "he said & he said" situation. The victim here was not asked for her testimony - which would have been truly direct, not any1 else's.
As for the "upheld" smoke&mirrors - the procedures of the lower court were upheld, not necessarily the lower-court opinion that Terri truly wanted to die.