Morgiana
Jealous of her vapidly "good" sister's popularity, poisonous Viktoria doses pretty Klara's tea with a slow-acting fatal substance. As the latter grows hysterically weak, the former finds success increasingly compromised by guilt, blackmail, and the pesky need to kill others lest she be exposed.
Starring Iva Janžurová, Josef Abrhám, Nina Divíšková, Petr Čepek, Josef Somr, Jiří Kodet, Jiří Lír, Ivan Palúch, Zuzana Fišárková, Marie Drahokoupilová
It's a crime and drama movie, and has a rating of 7.2 out of 10 from Imdb which is usually fine for this kind of movie.
Watch it here
Not found streaming from United States.