PleaseimLIN, don't give her that much importance in your lives.
It's pretty obvious that she would not do this, unless she wanted a reaction. You said yourself it's been a long time since there was any communication at all. Why now? you ask. Because she can. Because she knew it would generate negative thinking on your part.
I'm pretty sure she won't answer your email, but if she does take whatever she may say with a grain of salt..then let it go.
You've been working on your marriage for a few years now...dont let her even START to undo what you've both worked for with this email.
Even if she accidentally got hold of the email info, she didn't have to act on it....but she did....and that should say loads about her values. She knows you're back together and happy..so why pull this stunt.
Maybe the best thing you could do is sit down with your H and send an email TOGETHER to her, wishing her the best, and stating in no uncertain terms further communication is not necessary nor wanted by either of you....period.
Women are angels. And when someone breaks our wings, we simply continue to fly...on a broomstick. We are flexible