I think that was just an easy way of showing how a child going thru adolescence will "love" their parents one day then getting into their teenage angst years, they "hate" them for something as simple as not letting them borrow a car or something.

In the book Louise remembers/experiences the typical parent/child arguments as Hannah goes through her teenage years. I'm guessing that scene was the directors way of showing it

Yeah forgot about that bit, there was so much to take in. Seems a bit risky and irresponsible telling an 8 year old who was obviously very bright like her.

If she told Ian then she could have just as well told Hannah but I dont feel that happened. She hints at it however in 1 flashback where she tells her 8year daughter about a unstoppable disease but obviously at that age she is going to be oblivious.