Yes, these sentences are natural and poetic. Using "itself" in this way emphasizes that the subject embodies the quality completely, almost as if she is the perfect representation of it. However, while "cuteness," "beauty," and "love" sound elegant and commonly used this way, "braveness" might feel slightly awkward. The word "bravery" is more natural in this context.
Here’s how they can be refined for fluidity:
- **She is cuteness itself.** (Perfectly natural.)
- **She is beauty itself.** (Elegant and common phrasing.)
- **She is bravery itself.** (Sounds more natural than "braveness.")
- **She is love itself.** (Poetic and powerful.)
If you’re aiming for a poetic or formal tone, these are excellent. If you'd like more casual alternatives, feel free to ask!