Lost momma of a kindergarten

Keeping this anon as I'm ashamed to say I am a little embarrassed by this and feel like a failure as a mom. So my daughter (5.5 yrs old) started kindergarten beginning of September. She has always been the sweetest, kindest, calmest little girl. In pre school and preK her teachers raved about how amazingly well behaved she was and how well she used her words to talk through issues. She was polite to a fault and every kid loved playing with her and every parent loved having their kids play with her because of how bice she was. Same with sports or other activities...she was always the most polite and kindest and best behaved. For some reasons since school has started she has had issues on several occasions with hitting/pushing her classmates and most of them she was with ladt year for preK. We talk about it and she always says it's wrong and we don't hit and she knows it is not ok. But she has had 2 days where she has had multiple issues through the day and has needed reminders on other days. There are a few new kids who seem to also be hitting a lot and dont know if it is just copying or what but she doesnt hit at home or parks or sports or anywhere else but is still having issues at school. We talk every morning on our 20 minute walk about expectations of the day and how she is to keep her hands and feet to herself and she always tells me that she will and she knows it's wrong but we are still having issues at school only. I feel like I'm doing a bad job as a mom if I have the kid whose hitting and I don't know what to do as I know the amazingly sweet and kind little girl she is everywhere else whether I'm there or not and don't know why that same girl isn't at school. I want her to be successful in school but mostly I want her to ne a good human who is kind and I feel like a failure she is hurting others.