She was played by Amy Landon.
Yvette Ellison and her fraternal twin sister, Rebecca, were heiresses to their father's vast fortune, but when it is revealed that they have illegitimate half-siblings who stand to inherit a share of the money, Yvette went on a mission to kill them to prevent having to share her inheritance. Knowing that any evidence would be traced back to her, Yvette acquired the help of a doctor, who she was having an affair with, to put her in a medically induced coma. She would later be woken up by her doctor so she could kill one of her half-siblings, and then put back in the coma, only to be revived again to kill the other half-sibling. Knowing that Yvette is the killer, Sherlock blurts a random name after choreographing an altercation with Detective Bell, and Yvette falls for the trap and is caught and arrested. At episode's end, Sherlock tells a shocked Rebecca that Yvette still placed herself in the coma after killing both of their half-siblings; revealing that Yvette was planning to kill Rebecca so she would have no one to share the inheritance with.