I think that since this is causing you more stress, you should bring it up to her in your next session. I think that you and she should jointly agree how often you can email her, and what you can expect when you do. I think you have to get her involved in the boundary setting because I think you will always worry what she is thinking if you don't. Like you could think that emailing her twice a week was reasonable, but you might worry that she would still think that was too much and that she is angry with you.

Since she doesn't typically respond to your emails, I think it would be better to bring it up in person with her and say something like "I worry that I am annoying you with my emails, but at the same time they really help me. I wonder if we could talk about how often it is ok to write you because I'm getting really stressed about it."

I know it is stressful to bring stuff like that up with therapists, but I have found that nearly always I feel better after I do it. Because then I know what they are actually thinking, rather than what I imagine they are thinking.