I was just watching old episodes, episode 38 to be precise and there is a scene where Arnav is trying to remove the stain of the kumkum (I think that's what you call it the red powder) from his hand after he bumped into Khushi on the morning of Teej. Anjali asks him has the stain still not gone? Nani says that's why I always tell Chotey to be careful where you walk in life, you never know where you can get what stain and not every stain can be removed so easily.
Now I know that Aarav is going to be made out to be Arnav's son, but Sheetal will be lying. But it's so true what Nani said, if he was careful and didn't put himself in that position or situation to begin with there would never have been an issue to deal with, the issue that would stain his reputation, especially in front of his own family.
Anyway when she said that she was referring to Lavanya, but still the same rule applied to Sheetal too. But that must also mean Nani knew when her Grandson was up to no good.
I just wanted to share that with you all.