If anyone had the "glitch" where meridia's beacon would not show up on the map, I may have a solution. It happened to me and I had resigned myself to never getting meridia's artifact, but then, during the dark brotherhood quest, a ship appeared in solitude harbor (i won't spoil why) that was not there before and sure enough, meridia's beacon was on that ship. So not really a glitch, just an extremely unfortunate spawning location. If like me, the show on map button was greyed out so you couldn't find the beacon, try doing the dark brotherhood to completion and see if it works, good luck!
Thanks for the tip. That's why I read the forums, always like to be aware of "bug" averting situations.
On my previous character I found that beacon in a chest in a giant camp, like the other poster mentionned.