Source of Shubra's Insecurity

Various parenting references talk about the benefits of positive feedback for children. The reasoning is that if a child receives positive feedback from parents, he/she will more likely have better self esteem.

Looking at SP from this angle, what would make Shubra so insecure and susceptible to instigation (by Karan and Kaveri)? She supposedly had so much positive reinforcement growing up but still ultimately was weak in character.

Conversely, Saloni had more negative feedback throughout her childhood, yet somehow managed to emerge with a strong character.

What would explain this apparent anomaly? I have some thoughts on this but want to see what you all have to say.