Who is Elizabeth Bright Murdock from The High Window and what is their importance?

Elizabeth Bright Murdock is a wealthy widow. She is described as an imperious woman, who speaks directly and harshly. Elizabeth claims to have asthma, and she enjoys her port wine, which she says is medicinal. She hires Marlowe to get back a valuable coin that she believes has been stolen from her late husband's collection by her daughter-in-law, Linda Murdock.