Actually if you watch the episode...you'll see that she did catch this...She suspects that something is wrong, because obviously Chaturi was lying that she took her pay with her.
I was also wondering that Suraj just got his phone...so how would Chaturi know his number?
But never fear...Sandhya is already on alert and the precap showed her checking Chaturi's letter again. It had the postal mark of Maasa's village and not Chaturi's...so she suspects that Chaturi is in trouble.
I'm sure Sandhya will put all the clues together and get poor Chaturi off the hook soon.