- **She is capable**: Generally correct, but it’s incomplete. It sets up a situation or action she's capable of.
- **To do better**: This is where the error lies. The phrase "capable of doing better" should be used to indicate proficiency at something. "Capable to do better" is incorrect.
- **But she**: This is fine as it connects two ideas, emphasizing a contrast.
- **Lacks confidence**: Grammatically correct. It clearly states a shortcoming or missing quality.

The correct segment with an error is:
- ✅ **Option:4 - to do better**

**YOUR ANSWER IS RIGHT**