I don't believe that's so. The brain had suffered atrophy years ago and was stable. The missing tissue was replaced by a fluid, still present at her death.
For the autopsy, they had to soak Terri's brain in some chemical as they would anyone's brain that they had to look at and section, to make it firmer so that they can section the brain.
Not rehydrate her brain per se but this process is what they do to all brains they want to section.