Should she tell Maa Kamala what happened to Mala’s?

Are you referring to the stolen wedding veil? If so, Koly should be honest with her mother. Yes, Koly attended a party she was forbidden to attend, and yes, she put herself in a precarious position. She will likely be punished, but her punishment will likely be far greater if her mother hears the news from another source. If Koly is honest with her mother about what happened, and in addition tells her mother about the veil, she will at least garner her mother's trust, which will in turn, make Mala's accusations a non-issue. This is, of course, my opinion.