no worries... it is not a requirement for any exercise in any of Cathe's workouts, and not speaking FOR her, but she does state that you can use db's any time you want/need to in lieu of the bar...
sometimes a weighted vest can also help when db's are a bit too heavy to hold comfortably for lower body work... (some are adjustable from 10 #'s to over 100 #'s so you can find one that can be adjustable for you).
So, long story short... no a BB is not required if you have db's or other weights you want to use.