According to the official Witcher Twitter account, Patch 1.12 is now live. The patch fixes a whole host of issues that were preventing Witcher 3: Wild Hunt quests progressing or completing properly, including the notorious bug that prevented the Wild Rose Dethorned achievement from popping.
If you have cleared all those camps and still not grabbed the 35 Gamerscore, booting up the game after the patch is applied should solve this for you. So common was this bug that True Achievements gives Wild Rose Dethorned a TA Ratio of 3.94, meaning fewer than 1 in 5 players bagged the achievement.
— The Witcher (@witchergame) January 11, 2016
As stated in the tweet, the full patch notes are available online.