She has high hopes for science and Instagram.

“Dear Kim, When you read this, you'll be ten years older in the year 2025. I hope this is where you are."

So she's either hoping to still be alive, or she is writing a warning to a future in which time travel has been invented, and she is caught in alternate looping realities. This is indeed a dark fate for future Kim.

"When it comes to how you'll feel about your body, remember to be kind to yourself and enjoy how you look now because you're not getting any younger."
Sources: Glamour Magazine