I don't think there's much doubt your therapist is fine with emails from you, but it seems like the need to push yourself is adding more stress, causing you to need to email her (again, it's fine if you do--she's already said that). Is there another way to go at this without railroading yourself?

Instead of pushing through the exercise, could you just email that you're going to try something different, which is to go easy on yourself and take a break until your next appointment? I've found that not trying so hard to excel actually gets better results.