Alchemy. Sigrid had a perfume bottle and squirted herself with it. You had to have heard the bottle being squirted and recognized she smelt of powerful aromas. That’s why you didn’t realize she had used any sort of magic on you. She used your own senses against you and pulled you into her trap when it was obvious you wouldn’t be donating willingly.
Sigrid is the worst type of person. She doesn't see others as equals, or even people. She sees them only as tools to help her with whatever she wants. If you disagree with her... Well, you know what happened tonight. It could of been worse though. She could of seen you as some pesky adventurer instead of a gullible fool. And now she knows you're not so gullible.
Sigrid is dangerous. Don't you DARE go back into that building trying to get your items back without the help of some powerful people. Your best bet is to wait until Asotil comes back and get him to help you out. Even then I'm not sure if he'll be able to handle her. Look at what happend when you took your necklace off. You completely caught her off guard with your violent reaction and she was still able to calmly douse all of your flames and give you back the pendant.