Like most females in the show, Lady Fontaine is skinny. She wears a white dress which covers her feet, white gloves, a tag to signify her role, a black hat that covers her hair, and black and white shoulder pieces, which are presumably part of her dress.
Physical features include beady eyes, red lips, red cheek makeup, a strand of hair sticking out of her hat, and a large nose.
Lady Fontaine is usually strict. She expects every princess (including Cat) to act as a damsel in distress, and usually uses British-like slang. In Fashion Victims, when Lady Fontaine is under the BLK spell, she smiles when she shows Cat her new purse. Cat questions Lady Fontaine smiling, and realizes that everyone in Epic is under the BLK spell. This could suggest Lady Fontaine rarely smiles, and isn't a very joyful person.