Oh, I've lived a long time so I have developed quite a bit of magic skill. I like to prepare concoctions and I have acquired a good number of useful tools over the years. One of them is a magic mirror through which I can see anyone, and by which I can take their measure.
I have no qualms about who I serve. If they have money to give me, and the challenge is interesting enough, I will do it.
So one day a woman came in through the door. She looked quite haggard as if she were recovering from some illness that had drained all her power. She asked me to make a mask with the face of her stepdaughter. She wanted her own daughter to wear it so that she could step into the place of her sister who was about to become a princess.
I looked into my magic mirror and I saw the lovely girl, walking in the gardens, wearing a green silk dress. I took the precise measurements of her face, and made a mask that would fool even the most intimate lover, providing she wore a veil and said absolutely nothing.
You see, the unfortunate masked girl could only say "dirty creatures" whenever she opened her mouth. I thought it quite funny to imagine what would happen when the newly married husband approached his bride. He would be taken aback to be called a "dirty creature," do you not think?
Witch Who Makes a Mask in The Enchanted Wreath, Orange Fairy Book