What should I do about this situation with my boss?

Whoa now, not responding to one of your e-mails doesn't mean she thinks you're the worst employee on the planet! LOL Calm down, hun! It's not even the end of the workday yet, perhaps she's just been busy. If you've been a reliable employee for these past 3 1/2 years (which I'm sure you have been) then I seriously doubt your job is in jeopardy over something like this. If she never responds to the e-mail and this is still bugging you as much tomorrow morning, go have a quick word with her and just tell her you want her to know that you're once again sorry for not getting those news articles out as timely as you could have, and that you'll be double checking the website from now on to make sure you didn't miss anything.