- Materialism: She wants to have more things.
- Trying to impress her peers: Does she share her stolen goods with her classmates?
- She feels neglected and needs more attention: Has your attention been diverted recently because of a family crisis or problem?
- She may be seeking revenge on her teacher or you for some perceived mistreatment of her.
In addition to knowing your disappointment, your daughter needs to suffer the logical consequences of stealing. She must return what she steals to her teacher or her classmates and apologize for stealing these items. If she won't apologize, then you need to accompany her and speak for her. Speak to her teacher beforehand about your plans to come to school with your daughter.
All misbehavior, including stealing, has motives. You need to discover what your daughter hopes to gain from her actions. A good place to get those answers, if she continues to steal, is to examine your responses to her stealing.