Why is it hard for anne to confide in margot?

I think it was challenging for Anne to confide in Margot, because towards the beginning of her autobiography Anne was envious of her" talented" sister, and from my perspective it WOULD be difficult to confide in someone who is superior towards you. I also believe that Anne thought that Margot would judge her (preconceived notions) and misunderstand what point Anne was trying to make. :))