The owl will not deliver the doll to Clara, but will stick it on her. If she makes any attempt to thwart the owl in this respect, and swats at it, it will immediately explode on her. The doll has an impervious sticking charm, and any attempt at unsticking it (magical or otherwise) will cause it to explode, given the sensitive nature of the doll.
The inside of the doll (what will explode over Clara if there are attempts at removing it) is full of a creamed garlic, watery centre which has a potion in it that keeps the smell of garlic from leaking out. The creamed garlic inner is kept in a delicate tube that is charmed to explode the doll (explosion itself is harmless to all ~but~ the doll) ten seconds after the sticking charm is activated, which will cause the creamed garlic to get all over her.