The Perfect Assistant

The Perfect Assistant is a 2008 AmericanCanadian madefortelevision Drama film starring Josie Davis and Chris Potter .

His wife soon dies, due to an injection Rachel gives her. Then Rachel gives a stomach bug to Davids business partner, Judith Rachel Hunter, allowing her to go to New York with David.Rachel asks her cousin Nora, to watch her house while she is in New York. Noras computer crashes so she uses Rachels, who returns from New York and is angry to discover this. Nora confronts her, but Rachel kills her by pushing her down the stairs. Judith and coworker Wally tell their suspicions of Rachel to David, who later fires her. ........

Source: Wikipedia