Nida is shower w/love & adore by everyone & she get thing hand down to her effortlessly b/c she the apple of everyone eye. Since the beginning , Nida seen more scar of Saiparn than being a caring sister, she doesn't express pitty toward Saiparn. It was all fear of being bullied, just like the scene she let Napa took the blame while she ran & hide. No matter what happens, Nida will be protected by everyone, especially the Dad.
Saiparn haven't took anything from Nida yet until Poodit came along. Ppl who are bullied will eventually snap , of course she went crazy , b/c Saiparn stole her man , in her eye Saiparn is a bully , those other time wasn't anything serious for Nida to be angry about but now all those build up fear & selfish intervention make her unreasonable & oblivion to Saiparn 's misfortune , she continues to cling to Poodit & refuse to lose him even though what had transpired should had destroy any hope of a normal relationship but instead she is selfish , her own need & happiness come first .