As Mamazita said, watch for her cues - the face, squatting, passing gas, hiding...and nonchalantly take her quickly to the potty with an announcement "It's time to sit on the potty!"
Also take note of when she pees and poops and sit her on the potty just prior to those times, a schedule of sorts, after eating or drinking is generally pooping time.
For the record, my guy never told me when he needed to poop, I had to figure it out and get him there. He was fully trained @ 26 months, and now that he's 3.5 he still doesn't tell, unless we're out and he needs me to find a bathroom. His preschool has found the same, he just goes and does his thing...he likes to keep it private.