First of all, this is not proof of your insignificance. For example, my son is probably the most important person in my life. His wellbeing is one of my highest priorities. However, I still occasionally fail to respond to him in the ways that I should. I get busy or distracted, or I forget. But it doesn't mean I love or value him any less. (And, being four, he thinks EVERYTHING he says has life-or-death importance.)
The same is true with your T. She values you. But, for whatever reason, she didn't get around to reading your email. My rule of thumb is, if something like that really bothers me, I should bring it up in session. The more you try to ignore it, the more you'll just resent it. Go tonight and talk it out. She'll understand, and you'll most likely feel better.