history: I accidentally sent an email to a coworker saying that I was frustrated with her attitude. I wanted to dig myself in a hole. Unfortunately_comma_ I accidentally sent an email to a coworker essentially complaining about her attitude. I really wanted to dig myself in a hole and never come out. Arghhhhhhhhh! I soooo feel for you and have been there. Have y'all had the chance to talk about it? (Or do you even want to?)
current: I've kind of avoided her a bit. I'm trying to come up with an apology that feels heartfelt. It's a horrible feeling!
next: I hear you. Maybe humor might help? Like "okay, so *this* is awkward....can we talk about that email?" Heartfelt apologies go a long way, and even if she doesn't respond -- you'll feel better for trying.