Oh there will be an incident. *smiles micheviously*
Well basically, after Gandalf breaks the hold Saruman and Grima had on King Theoden. Grima takes matters into his own hands. He knows about Yavanna, via Saruman. Being whom she is and whom she is related to...makes her a target of certain enemies. 
The spell he would cast, would be a slow torturous spell. Kili would feel the affects first...before Yavanna would feel it. But she'd find an inner strength and with her knowledge of Elven Magic. She would fight him off. Her powers are still growing; she would tap into a very potent magic in that moment. But she would be rather weak from both his spell and the strength of her own magic, used to fight him off..Kili would need some recovery himself, just like Yavanna.
The scene would kind of replace/add to his banishment scene.