I agree with most of your points but I really do think that Riddhima is to blame for Armaan's state. At least partly. What exactly did she want to prove by giving her 'kasam' to him? I mean, what good did it do to him?! He just got beaten up because Riddhima still affects his life and her words mean a lot to him. It's because of her, he couldn't win the fight! If she really wanted to stop him, then she could've given him the 'kasam' of not going at all! And one more thing I didn't really understand was, why was she blaming Shilpa for not stopping him?! She herself knows Armaan the best and knows how he never listens to anyone but her so blaming Shilpa is useless! She couldn't stop him herself, so instead of blaming Shilpa (and her upbringing, childhood, personal life etc), she should try find a way to help Armaan rather than blackmail him! I just find Riddhima's character REALLY confusing, it's like not constant at all! It keeps changing!
On the other hand, Shilpa doesn't deserve to be treated this way! She's human too! It's said that "The girl with most unbreakable smile is the most vunerable". That phrase truly describes Shilpa! She's so brave, strong but from the inside, she's like a piece of delicate glass, which already has cracks in it due to childhood and this whole event just shatters the entire glass. She'll be completely broken! And she has no support whatsoever. I really feel bad for the poor girl!
Riddhima is so lucky to have everyone love her so much, yet she doesn't appreciate it enough. And there are people like Shilpa and Armaan out there that don't have any love in their life yet put on a mask of happiness to hide their sufferings just to make others happy!