Entirely okay, Apsm.
Gerald's change is, as you rightly said, triggered by such things as stress and arousal; though often acute and sudden in timing to make the transformation.
The transformation back to Gerald, the male form, that Jessica undergoes happens without any real trigger. Rather it happens varingly after several hours, though it can be expedited towards the end by some factors; and can also be impeded to a small extent too before transformation becomes inevitable for her.
I hope that answered things for you
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Alchemical Night.