She'll poo when she needs to. I'd recommend feeding her if it's her 'scheduled time' to feed. I notice many of my corns that get close to shed time will hold back a poo or two for one massive dukey after they've shed!
FYI, in my experience it's okay to offer food while in blue phase as well. The snake will let you know if they will eat or not. I have many that eat all the time every time, and I have a select few that will refuse prior to shedding.
D80