The events of Boruto: Naruto Next Generations have so far focused primarily on the development of its main character. His younger sister, Himawari, has so far been relegated to the role of supporting character. While this makes sense given that she's ten, after the timeskip, her role may change.
Despite not being a student at the Ninja Academy yet, Himawari's potential as a kunoichi is already clear, and it would be a shame if Masashi Kishimoto didn't make use of her post-timeskip, likely as a Genin.
Signs of Potential
There's palpable irony in the fact that Himawari and Boruto are both prodigies, in stark contrast to Naruto and Hinata, who worked hard to become powerful ninja despite lacking natural talent. Unlike Boruto, Himawari has inherited the Byakugan, and was able to activate it with no training at the age of six. She has learned to use it at will as of the current point in the story. On top of this, she was able to learn the Hygua Clan's Gentle Fist technique with no training, and was skillful enough at it to incapacitate her father.
If Himawari chooses to follow in her family's footsteps and become a ninja, it's a very real possibility that by the time she hits 13 (the age she will be in the timeskip), she may stand out the way her cousin Neji did in Naruto and Naruto Shippuden. This would mean learning to use techniques her mother couldn't initially master, like Eight Trigrams Sixty-Four Palms and Eight Trigrams: Palm Rotation. Combine this with the abnormally large chakra reserves of the Uzumaki clan, and you've got a recipe for an extremely powerful kunoichi.
A post-timeskip Himawari would likely be a Genin like her brother, but it's also a realistic possibility that she could make Chunin relatively soon after. Despite failing the exam twice, Boruto's abilities are certainly at least Chunin-level at 13, so it's feasible Himawari will be similar. Conversely, she could also potentially be an Academy Student, like Boruto was when the anime began. The former is, however, a far more compelling option.
What Will Happen to Himawari?
The brief post-timeskip scene at the beginning of Boruto makes it clear that he will be forced at some point to confront his adopted brother, Kawaki, who seeks to bring the Shinobi world to an end (or so he says). Himawari has also developed a strong relationship with Kawaki, and if he does indeed betray the Leaf Village, it will likely affect her deeply. The fact that Boruto is also a target for anyone seeking to plant a Divine Tree (be it Kara or an as-yet unrevealed Otsutsuki) would also be a weight on her mind.
Sad as it is to say, the foreshadowed tragedy at Boruto's beginning makes it hard to believe that Himawari will completely retain her cheerful and happy disposition. As a witness to her father's fight with Delta, a member of Kara, Himawari has now been exposed first-hand to the potential brutality of the world her brother and parents operate in. The danger that inevitably surrounds her family seems likely to make her a more serious person as she grows, hopefully without diminishing her kind heart.
Regardless, the biggest mistake Kishimoto and his team could make with Himawari post-timeskip is to continue using her like they are now. The very fact that she's Naruto's daughter makes her deserving of more than a supporting role. It would be incredibly gratifying to see her become a full-fledged ninja, and even more gratifying to see her fight alongside her brother at some point in the future. By contrast, using her simply to increase Boruto's cuteness factor would be a massive disappointment.