Very nice post.I agree with your comparison on Naina's difference in behaviour towards Sam and Swati.
But(as I had mentioned in a previous post)wasn't that the way she always behaved?If Naina hurts someone inadvertently and the person quietly accepted Naina's actions,Naina lets it go.If that person hurts her back,Naina immediately falls into the ocean of guilt and bends over backwards apologizing to them.This is just my observation from the way her character has been portrayed in all these episodes till date.
After getting caught by the police or when she left Sameer,Sameer never transferred the guilt or pain back to her.He could have done a 100 things to hurt her,but he didn't.He also did not malign,betray or gossip about her.If he had done that (just hypothetically)Naina would have reacted very differently and would have certainly apologized to Sameer.But since he didn't hurt her in return ,she didn't bother about it.
But Swati hit her where it hurts.So true to her character,Naina starts feeling guilty and is very sweet to Swati.I wouldn't be surprised if Naina goes further and apologizes to Swati in further episodes. Swati will ,of course,apologize to Naina,but Naina will also bend over backwards for her..I am sure we will see this in upcoming episodes.
It is strange,no doubt,but from what I have observed, it is the way she has been consistently behaving till date.