Briar, your boss sounds extremely unprofessional. How is it possibly in your best interest to inform you now of your assistant's pending termination? You are supposed to see this ax over her poor head every day and just wait for it to fall?
If that's not stressful, I don't know what is. She's implying that your job causes stress, therefore W/C and she wishes to exacerbate that? I am at a complete loss here.
I have way too much work, but it's never stressful. Each day I pick and choose what can be accomplished knowing that tomorrow is a new day.