You owned up to your mistakes - you screwed up the spell, it was entirely your fault that your girlfriend had been transformed into a kobold. The thing is, she was in no hurry to get changed back. For the past few days, she was acting a bit more manic than usual and starting to talk oddly, so you were concerned that it might be taking a toll on her mind, but she just laughed it off. It was true that these situations were usually fully reversible, but...the other aspect of it was her insatiable "appetite." Hard to imagine before that you'd ever have trouble keeping up with her, but here you were, exhausted for the fourth time today.
What was most concerning was how she'd started hinting that you should join her as a kobold, and that you were beginning to feel tempted...