I won't call her selfish. I would call her confused & immature.
That's just what she said on the surface, but if you look at the episode when Nikhil announced his engagement, she clearly was heartbroken. I don't think its fair to say that she doesn't care for Nikhil at all.. that's just her defence mechanism kicking in because she refuses to acknowledge the truth.
Myra has a similar problem. She blames Kabir at every opportunity because she is trying hard to fight every emotion she feels for him. He came into her life so suddenly, crushing her pride & making her act against her values.
Both Rhea & Myra need to learn that acknowledging the truth & admitting that you like someone even though he may not be the ideal you thought of does not show you as weak or settling for someone lesser. Everyone is flawed. You cannot choose who to fall in love with.