Well, I've read a lot of stuff but I don't see other solutions to this then those mentioned in two places:
http://forum.bioware.com/topic/22454-stone-prisoner-quest-not-showing-on-world-map/
http://help.ea.com/ca/article/my-dragon-age-origins-dlc-is-unauthorized-or-not-there/
And this:
When Dragon Age: Origins is first installed Steam runs some additional setup programs. However when you reinstall it later on the same machine Steam skips this part.
In this case the downloadable content isn't showing because it hasn't been properly added to AddIns.xml- you can fix this by running DAOU_UpdateAddinsXML_Steam.exe which is located in, by default, C:\Program Files (x86)\Steam\SteamApps\common\Dragon Age Ultimate Edition\redist.
I don't know what happens, but it seems that this has happened to people way back in 2009 already. Hope any of these ideas somehow helps you.
Also make sure you install the offer files with the updater, just placing them doesn't work. I doubt though that you haven't tried it all when I read your opening post.