Season 1 Finale: Why does she want to go back a second time? I get it that it's not nice to have to deal with your brother's death again, but in this timeline he's lived an extra 10, 15? years, and as far as is shown everything in your life is much better. You're more successful, your sister is not married to a loser, your brother's lived longer, your parents get on better and your dad's the writer of some Spock related best seller. What's your issue? Why go back and set up a time capsule letter?
Because she lost 10, 15 years of her life. Yes, things seem objectively better from the little she saw, but it's still not her life; she didn't live any of it and doesn't remember any of it.