As a human, Ruth mentions how similar Isabel and Chise look. Both have red hair, though Isabel wore her's in wavy curls. She says she has carrot hair and eyes that look like weeds.
As a chimera, her lower body is replaced by a spider-like body that has eight "legs". Each of these "legs" is made from an upper thigh, an arm, and a hand. There's also an additional set of arms in place of mandibles. Her lower body can also be opened in the form of a gaping mouth with teeth on both ends.
Isabel was a baby when Ruth met her. They stayed together through her childhood before a few boys chased her into an ongoing carriage. She died and was later dug up by Cartaphilus to use as part of his Chimera.