I remember reading threads about how you were looking for anything to help Sassy. So I don't think anyone would judge you or think you are just giving up on Sassy. If anything, you are doing the best thing for her. While it's the most difficult thing for YOU, you know it is necessary. Many of us have been there, or will be someday.
It took my mom months to finally make this decision with her Min Pin, Kodi. But now she is at peace with it and knows it was the best thing for him.

HUGS to you and your family.