Sapai Jao (2002)

Chai Rong is a royal who's betrothed to Srijitra, but loves Ying Koy. Despite Srijitra's acceptance and efforts to learn royal etiquette, Chai Rong ignores her. Srijitra finds solace with Chai Lek. When Salin, Srijitra's sister, goes to visit her at the palace and finds Chai Rong with Ying Koy, she tries to help her sister from the unwanted marriage. However, Salin and Chai Rong bond and eventually fall in love.