The day she realized her ambition was no longer to aid snow but to destroy her, Lady Adair knew her husband would never stand for it. He must step out of the picture. It never once occurred to her that he could perhaps be persuaded or that there may be other people who would support her. It is lonely when you believe all the world is judging you, and you feel as if you must act alone. And so she did, first to take the king out of the picture, then to remove Snow.
She didn't want to kill him, that would be counter productive. She needed his authority to do what she wished. Instead, she wanted him subdued. Weak. But since the king was a strong man by nature, this was more easily said than done.
In the end, she settled on a spell, simple but powerful, that would take a soul and focus it on a concept to plague his every thought.
The queen knew the dangers of this spell, and so carefully chose what his center was to be. After all, if he left behind his attachment to her, all might be lost. So, she chose his center to be her. But, because the focus must be a concept, not another soul, she chose her beauty.
She cast her spell. Those who should have protected the king from such a terrible curse had long ago lowered their guards. Lady Adair spent all her energies on Snow, she was no danger to the king.
How wrong they were.
The kings many sons noticed the shift, but mostly dismissed it. It matched the romantic ideal that a husband should think well of his wife. If anything, they rejoiced in what appeared to be a healed relationship.
And thus, Lady Adair became the ruling queen, in all but name.