I highly suggest converting to pellets. You say you feed seeds with fruits/veggies, but the plastic dish pictured has round, flat, rainbow pellets. Not sure what's going on here. The dyed/flavored pellets are not very healthy, I recommend Harrisons, roudybush, or almost any other unflavored and not dyed pellets. Cockatiels are grainavores so they should have seed in their diet, too, but not only seed.
That size of poop is definitely a normal sized morning poop, but you say it happens all throughout the day. Does she ever have smaller poop or is it only the big ones? How often does she poop?