Nice discussion going on here. I liked most of the view points presented here though they are differing from each other.
I haven't seen the episode. But, if Ragini has said that Khushi resembles Sadhna, then I do agree with that to an extent though not fully. Children inherit certain characters and learn some through the environment where they are brought up. Khushi certainly has inherited Sadhna's characters but Khushi's environment is definitely different than Sadhna's. Though both of them did not have parental love, Sadhna had a difficult childhood where as Khushi has a secured environment.
I feel, CTs want to show Khushi as Sadhna's roop. Hence, they are showing her sacrificing nature from childhood itself. I don't know whether this kind of nature is seen amongst children or not. But, I really don't appreciate CTs here. I would have liked it more if Ragini would have stopped Khushi from getting into this sacrificing mode from this age itself (I really don't know whether Ragini has stopped/will stop, as I haven't seen the episode). Ragini has seen due to Kaushi or the circumstance, Sadhna has suffered and she should ensure that Khushi (or Tamanna any one) should not get into sacrificing mode from this age itself.
Having said this, I do appreciate children who show their maturity with innocence. At the same time I would love to see them live their childhood with all the happiness.
These things are very subjective. What is right according to me may not be right for others.