Why is Sandhya taking all the decisions by herself?
She is just married and new to her in-laws house. She does not even know any of them well including Suraj.
She is seeing the circumstances and imagining everything negatively.
First, she came to know her brother's lies and she imagined her parents being blamed of their values because of these lies and she accepted the marriage.
Today, again seeing Meenakshi's parents' condition, she again imagined her brother and bhabhi in their place and could not bear that. Now...she is even not going to tell them that she is educated and HAS DECIDED to lead her whole life with these lies.
Why is she not understanding each and every situation is different and the approach definitely differs from person to person (my opinion). Bhabho may not treat Sandhya as she does with Meena and Sandhya is not as irresponsible as Meena.
In today's epi, she said Sandhya to forget about the robbery and try to be happy on the festival day and do all the decorations and pooja by herself (bahu) and all and she just turned and saw Meena and scolded her (another bahu) to just be in her room and not to come in front of her.
It is a very bad decision of Sandhya to do so. She should talk to them.