Hi,
I can understand you, we were in a similar situation 4 years ago with our dog (we are a dog-cat family). "Luckily" for us, we were on time to take him home for his last hours.
But, rage and sense of vengeance will never gave him back to us, neither will happen to you. On the other hand, I totally understand your pain, I'm on the verge of tears just remembering ours.
If you want to take any advice from an stranger like me, let's make people around you and them know what has happened, not with rage but with facts, and allow them to make their own decision.
For us, since that awful day I've never recommended that hellish place to anyone asking for advice or around us. But, honestly, people have challenges to be empathetic with rage, specially if it's a pain they have never endured.
Hope you can remember the best memories of her for many many years.