In Shrek 2, just before Shrek interrupts the Fairy Godmother (Dama Fortuna) making Love Potion No. 9 for Fiona, you can see 2 pictures of Doris the stepsister from earlier at the Poison Apple, one saying "Before" and one saying "After". The "Before" one is of her looking like a man and the "After" one is of her looking like a woman. But earlier in the film, Doris still looks like a male. So did The Fairy Godmother screw her over or something?
I don't see any problem here. In the "after" picture she appears much as she does when we see her in person in the tavern.
Note the high pencil-thin eyebrows, blue eyeshadow effect and rouged cheeks, visible in the second picture but not in the first. Clearly the Fairy Godmother's potion has been effective in turning this individual into an (ugly) woman. What's not clear is whether she was a man to begin with or just an even more ugly woman.