Elizabeth "Beth" Roney is the main villainess from "An Unnatural Arrangement," episode 2.06 of Elementary.
She was played by Sarah Wynter, who later appeared on Law & Order: SVU's 400th episode as the evil Dr. Nicole Keller.
Beth Roney is an archaeologist who oversaw a dig in Afghanistan, with James Monroe and Sam Clennon as partners. Further detail revealed that Beth was having an affair with Clennon, and when he was murdered, it was indicated that Beth's ex-husband, Cameron Hecht, killed him in a jealous rage. While it was true that Cameron killed Clennon, it was revealed that Cameron did so under the orders of Beth, who realized that the objects found at the digs were worth millions.
After stealing the collectibles, the evil Beth sent Cameron to kill both Clennon and Monroe, all the while reconciling with Cameron and forming a partnership with him. Beth managed to cover her tracks by hiding one of the objects, after Sherlock noticed it out in the open when he and Watson first visited her home. In the episode's climax, Sherlock and Watson returned with Detective Bell to arrest Beth, after they talked to Cameron. Sherlock stated that Cameron gave up Beth, and it was Beth's dog, Gotham, that gave both of them away. Beth stated earlier that Gotham barks at nearly any man who came near her home, but Cameron was the one exception. The villainous archaeologist was later handcuffed and arrested.