The difference is the one between negligence and manslaughter. If your negligent actions result in something else down the line, you are still, in part, responsible.
There can, and usually is, more than 100% blame to go around.
She wrote: "I'm sorry to hear your employer deciding to not to work with you on this and I hope they reconsider, bring you back on and dealing with it constructively." (emphasis mine)
I think that's the most we can expect from her regarding the guy getting fired. She didn't fire him, and she clearly expressed that she didn't think he should have been fired over this.
There can, and usually is, more than 100% blame to go around.