When I read your post, my mind flashed straightaway to the exact spot (behind her bedroom door) that DD2 used to crouch. I found it helpful to talk to her about how her body might be feeling right before a poo starts coming out & how that feeling means its a good time to go and sit on the toilet so the poo comes out & goes in the toilet instead. regardless of what their TT "readiness" is, talking about it helps normalise using the toilet.