The % is very low to get the drop. And it does not keep a counter on how many non drops you had. What that means is if it is @1%, then it is 1% every time you kill it.
Try different days. This is typical. Not a bug or an issue, welcome to the world of conan exiles. The trick to have everything every single boss has, is to try the same boss 3 times the day for a week. So make a schedule which bosses you want to farm this week and keep farming them for at least 3 times. Believe me, you will get so many torches that you will fill a small chest, ofcurce not in a week but if you all ready posses more than 2 then it is pop corn. Last but not least, play on the same server all the time.
It is not bugged, just the lottery from hell. It can take a very long time to obtain one specific item off her, unless of course it is twine. Fieldbreaker I was literally going through the same until quite recently, and I hate to say that it took me over 7 months to grind one. Part of he problem is that her loot tables are full of superfulous items in addition to the Legendaries, such as bowls and iron bars.
As I state in the below thread, Funcom should consider 2 courses of action: I) remove the lower level loot from her loot tables II) reassign some of her Legendaries to the Green Dragon and the White Dragon, who have 0 unique drops, and as such no real incentive to battle them outside of novelty value.