She's threatened and insecure by Saloni's self respect and kindness. She thinks she's arrogant and being "ugly" has no right to have any love or esteem.
Shubra, i've noticed is jealous of Saloni because their Dad seems to be closer to her than Shubra, plus Shubra's also taking her insecurities out on her...although she's "fairer", Saloni is well educated, talented and has confidence. Something none of them do, really.