Awesome chapter I really enjoyed it, keep it up.

It was humiliating to soil herself in front of others. It was shameful to allow herself to have an accident like a foal. But at the same time...it was incredibly, undeniably arousing!

I would think Fluttershy would still try to fight it as hard as she can. Part from habit but also because that's more exciting. Fight with all your might but have it still happen. Maybe even roleplay that she's constipated to get Mrs. Cake's affection.