Wow, the response to your email was very unprofessional and unsympathetic!
I'm so sorry this happened to you and your roommate. I can't imagine what it would be like... the excitement of opening the package only to find a dead and decomposing pet. Not to mention she completely ignored your perfectly logical concerns of the state he was in. She just got on defense and put the blame on you. Yes, there is a risk in priority shipping, but that doesn't dismiss the condition he arrived in.
P.S. Welcome to the forum, Summer!