Its very much possible that she's tara's half-sister. But she has a dark and wild side, that only the father has known so Jiji had threatened him to keep it a secret or else... 😡
So I'm sure Jiji must have done somthing very criminal-like to someone in the family, which only the father has been an eye-witness to, which explains his spooked look when jiji entered. just being adopted shouldn't spook him this much! he could have told the raaz a long time ago, but now that Jiji has gotten close to Tara's family by having a baby, he wanted to forewarn her. I think this is a good possibility because he could have told her the raaz b4 but the situation was not as dire as now.