One witch isn't supposed to be able to undo another witch's spell, yet Samantha turns Clyde from a chair back into a human when she wasn't the one who changed him in the first place.
It was explained early on in the series that a witch could undo another witch's spell if she knew what the spell was or how the first witch did what she did.
It was explained early on in the series that a witch could undo another witch's spell if she knew what the spell was or how the first witch did what she did.
The plot never explains why Samantha couldn't simply make a copy of the chair (using witchcraft) to send to Mrs. Cosgrove.