I think it would be better to call. Email can be misinterpreted. The thoughts you are having are pretty common. I think if you clarified for your T that you want the suffering of the fear etc to end, not your life to end, but you can't seem to see a way past the fear, she would understand you don't have suicidal intent.
My mom used to tell me to go kill myself when she was mad. Eventually I tried. I am much much healthier now but those lessons sunk deep. Those thoughts still come into my head with some frequency. My T and I talk about them and she never freaks out. She knows I lack the INTENT to die. I'm just still learning how to heal.from my past.

But email is tricky. Too many ways to be misunderstood. Better to call or schedule an earlier appointment and talk about it sooner