First, I notice her conversation with Dida was not shown. She most had told Dida the whole truth for Dida to show this much support to an extant of calling Laksh "beta"
Secondly, Since we all know that Swara also thought of her sister's feeling first before Laksh. then, how could she have taken such a step of billing Laksh without talking to Ragani?. Except, that she knows about how Ragani wants to take the glory of trusting Laksh to make him fall for her.
Lastly, I notice that when she talked about leaving the home with Laksh, a home she fought hard to build, , Her eyes was on Ragani. its like she is trying to say " anyway, I dont believe we are family anymore "
Since she has no prove, she has to work with what she already know.
Now, she is going to use Ragina's fake innocence to her advantage. Since she knows Ragani's nature of panicking, she will keep telling her her steps...but she will have her own silent twist to it. I am sure Ragani and Sanskar will fall for that trap.