You've already recognized the pattern. Now, when you send her an email, before anxiety kicks in, plan out a realistic anxiety schedule. You tell yourself, "I am sending this now, and I recognize that she might not respond tonight. Or tomorrow. But she usually replies within three days. If she hasn't written back in four days I'll be justified in feeling anxious." Precommit so you're not constantly thinking, "It's been 7 hours. That probably means it's anxiety time, right?"