Hey Arnold! (1996)

S3E10 Olga Gets Engaged

Olga becomes engaged to a con artist who doesn't charm Helga like he did with the rest of her family. Although Helga initially relishes the idea of Olga's impending misery, Arnold's words inspire her to reconsider. Determined to prevent the wedding, Helga sets out to thwart the engagement and save her sister from a life of unhappiness.