Hi Lauren,
I was just poking around in your blog, in case you saw me in there :)
So, I think the problem is that you had a featured image set on the blog. Often, a set featured image will pull that post into a special "sticky" area, and then the post won't repeat in the blog timeline. I didn't see a featured post area on your blog, so that may be a setting you'd have to set in your Theme settings.
But it looks like you were able to solve the issue by re-posting the entry without the featured image anyway. You can safely categorize it, if you so wish.
Also, you may not realize that you can "back date" posts - you can do this in the module immediately to the left of the edit post area - see where it says "Published on:"? You can change the date and time to make the post show up when you'd like (even if that's in the past)!
Finally, I also have a dog named Mac, but my guy is about 11 (he's a rescue, so I'm not sure), and is a red and white Irish setter. Your Mac is adorable!
Let me know if that helps you at all,
Cheers!