My cats nibble on all my houseplants.
Is China Doll Poisonous to Cats?
If your cats have nibbled and not become seriously ill, they're probably not seriously allergic to any of your plants. I can't find China doll (radermachera) on any of the toxic lists in any case. This article has some more information: https://www.gardeningknowhow.com/plant-problems/environmental/plants-toxic-to-cats.htm