its good to see Ragini that you atlast uttered "Sadhna meri bahen hain"....keep it up...dont try to compete with your sister's goodness and land up in an ego issue to prove your greatness and to show how you reciprocated Sadhna's goodness, RATHER feel proud that a noble soul like Sadhna is your sister....
In our society, very often, if we are related to a minister/ celebrity, we boast about it. Ragini boast about your sister, her goodness to everyone, tell everyone in cluding Kaushi that "Sadhna is my own sister and I am proud of my sister. I love my sister and will support her through think and thin"....its time that you speak like your father says that he has two daughters, not one daughter and one niece.
good luck