Dr. Franny Krieg (Emily Dorsch) was a villainess from "Pick Your Poison," episode 5.10 of Elementary (airdate December 18, 2016). She was a physician and a former colleague of Joan Watson.
As revealed early on, Franny was also a greedy identity thief who ran a "pill mill," selling illegal prescriptions to addicts and stealing the identities of other physicians to run her operation. Among many others, the villainous Krieg stole Joan's identity, and her actions led to the latter being investigated by the DEA and her license being suspended.
At some point, she was contacted by Marla Ridgely Moore regarding her son Ethan, who apparently had an autoimmune disease that left him barely mobile. Upon close examination, Krieg discovered no evidence of such a disease and that his mother had been poisoning him, with her clinic being one of many she had been doctor shopping at for medications to use for said poisoning. Franny even confessed to everything she had done during a private session with Ethan as she informed him about her suspicions. Days later, he returned to her office and shot Marla to death in anger, after which he murdered his physician as well since she would have told the police about what he had done.