Actually she got her father MS arrested once for same offence (prawns allergy issue), I'm not sure what stops her now.
Yes Ram has to prove he trusts her and being better husband, before she can trust him. But knowing her she didn't need to wait for Ram as she heard that MS is trying to kill Ram, for a principled person she needs to act on this and file a report at least. Given this is happening second time, it's even more unfair to hide this from Ram and everyone else.
The police was also looking into it, then why she wants to investigate herself and not go to police is a little hard for me to understand. As of now they can even look for proof but as time goes that's also hard to find.
I think she is not saying anything about her father this time because last time she had a proof that her brother did it and her father took the blame. This time she heard her father talking to someone on the phone and she doesn't want to aleart her father's accomplice by getting Mahendra arrested. The other person can go MIA and will never be detected and the danger will still lurk on ram.
Also she doesn't trust Ram or the Kapoors to not blame her or her family in this matter. And she is right to be sceptical about Kapoors .they will use this information to manipulate ram again.