Any boss soul? I.e those she actually needs to get to give you the weapons? That doesn't work for me, because I have the souls I need for the weapons on me, but can't trade 'em in.
Only certain souls Straid and her trade for boss weapons so if you have a boss soul and one doesnt do anything with it go to the other and he/she will. Straid tends to handle most of the early bosses and mid-bosses While Ornifex will handle all the old souls and the boss souls AFTER you kill all 4 old souls.
So for example Mirror Knight soul is used by Ornifex Dragonrider by Straid Old DragonSlayer by Ornifex
and so on. Basically take a look and if you dont see yours go to another. --- I have an answer to everything whether its a good answer is entirely irrelevant