Sapai Pateevat

Pawinee's sister is married but she suffered abuse from her mother-in-law, who looked down on her. She dies and leaves her kid behind. Pawinee is angry for the way the mother-in-law treated her sister, so she comes to the city and marries her sister's ex in order to take care of her nephew. The mother-in-law tries to outsmart her, but Pawinee always comes out on top.
(Source: MDL)
~~ Adapted from the novel "Saphai" (สะใภ้) by Nantana Weerachon (นันทนา วีระชน).