While Ridhima was her brilliant illogical self, I think I can understand some of where she was coming from on the staircase. While a woman of greater maturity and security may have handled it better (and dont we know that Ridhima doesn't fall in that category?), I can understand,though not appreciate, some of what she is going through.(There is a possibility that after reading this, Anu might def kill me and some of you might like to join in as well!!)
While creatives may have rushed thru the adoption bit, she has gone through a tremendous emotional upheaval, Armaan let her down with the bet business, and, then she felt the need to lash out at him cos even he was aware of her adopted status while she was blissfully unaware.
Now while she has accepted that she loves the guy, she still has to deal with her fears, and a very real one being that she is not Armaan's type. While she may have used the term "seedha sadha" I think both Armaan and she know what she is talking about. In that context, his numerous relationships, his obvious ease in and his enjoyment of women's company, his reputation as a skirt chaser, and the inability to really believe that he could love her, probably drives her inner demons which she grappling with. Hiding the relationship could be one way of avoiding the heartache, embarresment if things dont work out (someone needs to tell her that in relationships you need to take risks!!)
When Armaan forces the issue, her instinct for self preservation makes her lash out with that stupid, inane comment about her having a re-think. I doubt if she really meant it, it was the only hurtful thing she could think of saying when the guy is shaking her with exasperation and trying to force her hand in revealing their relationship.
Her obvious repentence immediately after he leaves, her unhappiness at being ignored are indications of the fact that she loves the guy but being the stubborn, opiniated person that she is, she is unable to back down or reach out. Even the line "to kyon nahi karte ho" to me sounded more like a plea to have things get back to normal rather than asking the guy to run after her again.
But all said and done, every human being has their own demons and insecuirities and has to learn to deal with them, and, so must Doc Ridhima. Otherwise, she might find herself having the lost the one thing which means the most to her..