I actually think that the curse is brought by her. She's the one that cursed Theodore because of his "betrayal". In fact, the first words she says to Therodre is saying that she curses Theodore. Until she finally lets go of her past and finally moves forward, I don't think that the curse will break.
@HOOfan_1 she wasn't looking for the answer for the curse , she is looking in the history of his family to know who applicated the curse and for which reason
In a few days the maids will just be :
Maid A : The Duke turned back into a human today as well !
Maid B : 'kay.
Maid C : Help us prepare breakfast already.