I have seen my own bile production bottom out on two separate flushes... there does not seem to be a rhyme or reason to it.
She may handle it fine and it will have minimal effect on bile production, in which case the following nights dose would be just fine... just pay attention each day after the dosing. She may want to prepare for being up and going to the restroom at night too... Castor oil has a way of hitting a few hours after dosing.