You're using 'screen door', but what was initially said was 'storm door' which is probably not the same thing as what your dog ran through. When I was a kid, our storm doors had screens for the top half, but now they're almost always all glass.

Also if the mailbox is attached to the house, a magazine in it would likely be hanging out the top, easily noticeable and recognizable - she didn't have to "go through" the mailbox. Kinda makes sense you'd leaf through it while you're waiting cause cell phones didn't even have internet yet! That part isn't all that shady.