Did the CVs forget that the first time Asad saw her, she had mehendi on her hands. It was not burned or anything. So, if she is allergic to mehendi, she didn't go through this for just Asad. She did it in her adhoori nikah also.
It doesn't make anything special isn't it?
I understand there was no other way of ending this scene without Zoya making a fool of herself if she had blamed Tanveer, but they could've got creative.