At that time sex and bodies weren't discussed. It was too private and inappropriate for a girl her age to talk about it. She was barely 13 and curious thats all. Today we see all that in magazines TVs and internet. Long ago they didnt have that.
Why Did Anne Frank Want To Touch Her Friends Breasts?
Because she was horny and lesbian
I do not believe she did want to touch her friends' breasts. You might want to research that.