Becca, I am so sorry for your loss. I certainly understand your pain.
Without knowing more about your kitty's affliction, it's hard to say how best to deal with this vet or the clinic. It's unfortunate that she blew it off like that. I've certainly been to better and worse vets over the years and have been frustrated myself when they didn't discuss an obvious test or react urgently enough to what seemed like an emergency to me.
Spend some time thinking about what course of action or inaction will help you and your daughter heal from this loss. From there, hopefully you can decide on how best to proceed.
((((((())))))).
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher