Yeah she is but I think she has her reasons sorta. Much more than her sister Yam in Sood Kaen where Donut was innocent. And yeah! I see P'Ratklao aka Yam in the teaser.
First, cause Reynu truly is a bonafide prostitute. What mom would want their son with a prostitute in such a conservative society? Second, Reynu got a black magic love potion put on both Phet and later Yoi too.
So I don't think Yoi is totally crazy for hating her. And Reynu's got an attitude. In the BTS special around 11:00 did you guys notice it's not Yoi slapping Reynu. But Reynu grabbing Yoi's hands to make it look that way so she can get sympathy from her dad-in-law? This girl lol.