What is a quote describing Mrs. Lockton's appearance?

The best place to look for a single quotation that describes Madam Lockton's appearance is chapter 3. It is in this chapter that Isabel and Ruth first meet Mr. Lockton and Madame Lockton. Consequently, Isabel gives readers a solid physical description of Madame Lockton. She is described as "thin." Following that is a description of her plum-colored dress, and readers are told that her general appearance gives the impression of wealth. Isabel believes that Madame Lockton is around the age of forty-five. She has small eyes and pale features. 

A thin woman stood next to Mr. Robert.  Her plum-colored gown was crisp and well sewn, and expensive lace trailed from the small cap on her head. She was perhaps five and forty years, with pale eyebrows and small eyes like apple seeds.  A fading yellow bruise circled her right wrist like a bracelet.

The final detail in that paragraph about the faded bruise is important foreshadowing. We don't know why she would have a bruise, but the fact that it is mentioned is important.  Madame Lockton's marriage is not a healthy one despite the public appearance that it may have. Mr. Lockton is an abusive husband, and Madame Lockton is not averse to firing back with violence of her own.