mmmm I would suggest asking her if she has done a poo rather then leaving her to tell you. She may not tell you & possibly end up with a bit of a rash if its not cleaned up ASAP.
Another thing I do with Glenn is ask him, Have you done a poo? He will say yes & then I will say Poos go in the toilet, Where do poos go? So he tells me Poos go in the toilet. then I clean him up & ask him if he needs to go to the loo.
It can be very frustrating but pushing TT on them before they are ready wont make it happen any faster. Just means you will be TT for longer.
Sounds like she is waiting for that moment when your busy with bub & she can go do her thing, do you think maybe if you stripped her off & sat her on the potty before you sat down to feed so she can sit there while you feed & do her poo?