Mandy's known as the "gossip queen" of the country club she belongs to and the gated community that she lives in. She was on the women's committee at her country club with murder victim, Scarlett Marquesa, who was the chairwoman.
When Jane and Rigsby went to her to see if Victor, Scarlett's husband, was having an affair with Asra Hadami, Mandy laughs off the idea, explains that Asra and Victor are just friends. Mandy then tells Jane and Rigsby that she thinks Victor was the one who murdered Scarlett---pointing out that while Victor's a nice guy, most of the time when married women are murdered, it's their husbands who murdered them, which Jane and Rigsby agree that she has a point on.
It's later revealed why Mandy laughed off the idea of Asra having an affair with Victor: turns out that Mandy and Asra are lesbians and that Mandy's been having an affair with Asra behind her husband's back.