Ah...Sarah honestly didn't expect this.
When she told Joseph about her uncle, she was just trying to probe their relationship, whether or not they were involved in whatever scheme they had with Daesung. When she told Lee Hyun that Joseph knew about the visit, she wanted to instigate some kind of fight that might destroy either of their plans.
She certainly never thought it would result in Lee Hyun being accused of leaking the CCTV to sneak buy HS's stock—exactly what she was doing.
Hearing someone else being accused of her 'crime'...it almost made Sarah lose control of her act. Thankfully, she could easily cover it by faking a gasp and clasping her mouth, stifling any laughter that might spill out. Hajin even helped her by pretending to soothe her--since she was coughing earlier--and gave her another cup of tea so she could calm her facial muscles further behind the drink.
